There are over 130,000 apps in the App Store. About 100,000 of those expect you to pay cash money for a download. Sometimes it's worth it! Often, it's not. Prof. Dealzmodo's here to help you tell the difference.

Oscar Wilde was right about cynics: they know the cost of everything and the value of nothing. On your next trip to the App Store, don't be cynical. Be smart—even if it means spending a little money.

The App Store Effect Is Real. Use It.

Last fall, John pondered the App Store Effect, which holds that Apple's model results in price deflation so severe that it's unsustainable... in the long term. In the short term, though, it's your ticket to apps that cost far less than their analog (or web-only) counterparts. And sometimes, they'll include even more functionality.

Examples? Certainly! Here's a range of apps, from professional to gaming to reference to navigation, that'll save you anywhere from a few bucks to a few thousand:

It's probably most helpful to think of these in terms of the broad categories where you're most likely to find a cheaper app alternative.

Hobbyist: If it's an activity that at least a few thousand people enjoy, there's likely an app catering to it. GuitarToolkit's a perfect—if extreme—example. For $10, you get a library of over 500,000 chords, a chromatic tuner, and a metronome. Purchasing all those items individually gets expensive and, more importantly, bulky. An app? A fifth (or less) of the cost, all stored in your phone. Frequent traveler? Download HearPlanet's collection of over 250,000 audio guides instead of shelling out around $8 for one at each location. If you have a common passion, someone's developing for it.

Professional: BarMax costs as much as an App Store product is allowed to, but the law exam prep app is still $2,000 less than an in-classroom service like BarBri. In fact, shortly after BarMax was released, BarBri retooled its pricing structure to be more competitive. It wasn't a coincidence. And other professionals—including pilots and nurses—have a bevy of targeted apps to choose from as well.

Cannibalistic: Companies are so eager to be represented in the App Store that they'll undercut themselves to be players there. An online subscription to Zagat.com costs $25 per year. The Zagat to Go app costs just $10, and includes location services and an offline mode that the Zagat website doesn't. You can play Grand Theft Auto: Chinatown Wars for $30 on the PSP, but it's only $10 on your iPhone. And Major League Baseball's MLB.com at Bat app lets you stream games for $1 a pop, while MLB.TV charges $99 for a yearly subscription. Sure, if you watch a hundred or more baseball games a year on your iPod Touch's tiny screen you'll want to go with the latter, but the pay as you go option is ideal for the casual fan with a vested interest in his eyesight.

Remember: with so many developers targeting the App Store, it's more than likely that there really is an app for that. But wait... what if there are several apps for that? How do you choose the right one?

App Overlap

Because the App Store is such a big ecosystem, it's inevitable that there are redundant applications. Some categories see more overlap than others, but in general it's common to find multiple apps that do the same thing. So where does the cost difference come from?

Functionality: The most basic—and most obvious—reason for an app to be more expensive is that it can flat-out do more. A casual Twitter user might be happy using Echofon for free, but if you need support for multiple accounts and the cleanest UI around, you're going to be happy coughing up three bucks for Tweetie 2. Make sure to read up on the full feature set of what you're buying. If you're about to pay for something with more firepower than you need, there's likely a free (or cheaper) version that'll suit your purposes. The paid app will still be there if you decide you need more functionality down the road.

Ad Support: Often, and particularly with casual games, the only difference between the free and paid versions of an app is whether you'll be saddled with advertisements as you use it. It really depends on your threshold: is it worth three dollars to play Words With Friends unfettered, or are you willing to endure the between-turn sales pitches that accompany Words With Friends Free? Each app integrates ads differently, so it's worth trying out the free version first. Too many banners cluttering your screen? You're only a click away from an upgrade.

Ripoffs: It might be helpful to think of the App Store as a giant, unruly bazaar, with thousands of vendors peddling their wares. There's some oversight when things get out of hand, but even the $999 "I Am Rich" app was downloaded eight times before it got shut down. Like in any sales environment, it's important to remember that what something costs usually has very little to do with what it's worth. Don't just go by the star system; read through the reviews to make sure that the app lives up to the developer's description.

Easier Said Than Done?

There's no question that a little research should go into whatever app you buy—starting with our Essential iPhone Apps Directory. Beyond that, here are a few common App Store categories with stand-out expensive, cheap, and free apps, along with our recommendations of when it's worth it to pay up:

Cooking

Expensive: 20 Minute Meals - Jamie Oliver ($8)
Verdict: Don't Download

Cheaper: Martha's Everyday Food ($1)
Verdict: Don't Download

Free: Epicurious
Verdict: Download
Jamie Oliver and Martha Stewart are powerful brands, but that's pretty much all you're paying for. Epicurious has thousands of recipes—including from famous chefs featured in Gourmet and Bon Appetit—a shopping list feature, and will suggest meals based on the ingredients you have handy. It's really the only cooking app you'll ever need.

File Storage

Expensive: Air Sharing Pro ($10)
Verdict: Don't Download

Cheaper: Air Sharing ($3)
Verdict: Download

Free: Dropbox
Verdict: It Depends
While Air Sharing Pro includes printing and emailing, the regular version should get the job done for most people: you can transfer your files to your iPhone's flash memory via Wi-Fi for storage and transport. The trouble with the "free" option, Dropbox, is that it's not a standalone app. However, when you link it to your Dropbox account you can share and sync up to 2GB of files for free. It's good if you already have an account, but if you don't, you probably should skip it.

Messaging

Expensive: BeejiveIM ($10)
Verdict: Download

Cheaper: AIM ($3)
Verdict: Don't Download

Free: Meebo
Verdict: Download
It might sound crazy to pay ten dollars for a messaging app, and for a lot of people it would be. But if messaging is your primary mode of communication, BeejiveIM's multi-account management, intuitive interface, and seamless push implementation are well worth it. For more casual IMers, it's hard to beat Meebo's multiprotocol support and push notifications. They even log your conversations on their servers. Another solid free option is Fring, which includes Skype support. What you don't want is to pay $3 for a messaging app like AIM, which only supports services on the AIM network and Facebook and is missing some features—like blocking contacts—found on the desktop version.

Navigation

Expensive: Navigon MobileNavigator ($90)
Verdict: Don't Download

Cheaper: MotionX GPS Drive ($1)
Verdict: Download

Free: Waze
Verdict: Don't Download
Just to be clear: Navigon makes one of the best navigation apps out there. But MotionX GPS Drive is a very good navigation app at a tiny fraction of the cost. So before you spend $90 on a top-flight turn-by-turn system, spend a few weeks figuring out if MotionX is good enough for your purposes. Chances are it is. And if it's not? It was worth a dollar to find out. As for Waze, anyone who's ever dealt with a backseat driver should appreciate just how unreliable—and aggravating—crowdsourced navigation can be.

Personal Finance

Expensive: PocketMoney ($5)
Verdict: Don't Download

Cheaper: MoneyBook ($3)
Verdict: Don't Download

Free: Mint.com
Verdict: Download
The first rule of money management: don't pay for something you can get for free. Apps like PocketMoney and MoneyBook aren't bad at what they do, they're just look a bit hypocritical with Mint.com Personal Finance around. Mint automatically syncs to your online accounts to help you keep track your budget and investments. It's the best personal finance app out there, and not just because it's free.

RSS Reader

Expensive: NewsRack ($5)
Verdict: Download

Cheaper: Reeder ($3)
Verdict: Don't Download

Free: NetNewsWire
Verdict: Download
You can get by with a free RSS reader, and NetNewsWire's a great option that syncs with Google Reader. Like the majority of free options, though, it can be a bit sluggish and prone to crashing, especially if you're loaded up on feeds. Among the paid apps, NewsRack (formerly Newsstand) shines for its reliability and speed. In-between options like Reeder? Well, if the developer's best troubleshooting suggestion is to limit the number of items you have to sync, you're not getting what you paid for.

Twitter

Expensive: Twitterrific ($5)
Verdict: Don't Download

Cheaper: Tweetie 2 ($3)
Verdict: Download

Free: Echofon
Verdict: Download
Tweetie 2 is our favorite Twitter app : it's fast, intuitive, and loaded with features. I can understand if you'd rather not pay to use Twitter on your phone, and Echofon's a more than capable free alternative. But only a twit would pay $5 for Twitterrific when the class of the field is just $3.

The Value and the Cost

Remember that the App Effect is working for you, at least for now, and that we're in an age of unprecedented deals on app content and services. Try not even looking at the price at first. Start with the feature set, see what's comparable. If it's free? Great! But even if it's $10 or $20, it still might be a steal.

We've gotten to a point where it feels almost perverse to pay for an app. But think of it in a larger context: you're buying software. On your desktop, that used to—and often still does—command exorbitant sums. Even on mobile platforms, Windows Mobile and Blackberry apps used to cost 10 or 20 times the average App Store paid download. Comparatively, App store downloads are peanuts.

And remember, too, that by paying for apps that are actually worth the money, you end up supporting the developers that are delivering innovative content and services. That means a better app experience down the road for all of us. Even the cynics.