The most I’ve paid for an app is $9.99. I’m hard pressed to name an app I might consider buying that costs more than that. However, if you do, here’s an Android app that might be worth its relatively high $28.99 price:
Oxford Advanced Learner’s Dictionary (Google Play)
A version is also available for the iPhone and is being developed for Windows Phone.
Oxford Advanced Learner’s Dictionary
Note that this app is not the full OED. The complete OED covers more than 600,000 words. This app includes less than a third of that number (184,500). On the other hand, the OED Online version costs $295 per year for a subscription. The Android and iPhone apps are priced at $28.99.
Is it worth it? I have no idea since I have not tried either release. And, there aren’t enough customer reviews on either site to draw a conclusion. Still, if words are your thing, it is a good-sized subset of the OED.
NOTE: Curiously, the iOS version weighs in at 412MB while the Android version is a featherweight at a mere 2.8MB. The Android version’s product page notes that it requires network access. So, it might not be suitable if you need to use it when not in range of 3G or WiFi access.