The really expensive iOS apps are mostly medical. Same story with Android. Medical, security, and GPS apps seem to be the most money. For the most part I'd say the Android apps are much cheaper than iOS apps. Just going through the market the other day showed me a thousand things which looked really fun that would have been at least $.99 in the app market.
Besides, with all of the 'black market' apps available out there which let you download cracked apps for free, the cost really isn't an issue for many people. I will say that paying for Easy Tether, Logmein, and Documents to Go has been worth every single penny. I've probably got about $100 tied up in ridiculously functional apps for my Android. I love my phone more than my car at this very moment...