It's clear that selling an app outright is a tough proposition for many independent developers. Your biggest challenge is getting downloads and building momentum for your app. The easiest way to do that is to offer a free app and build in the ability for your user to make a purchase after they've downloaded and used your app.
Everyone loves free! Unless you have huge brand recognition or get real lucky with your app going viral, you should take a serious look at making your app free on the front end and charging people on the back.
It's a sales model that's worked for thousands of products over hundreds of years. So, why not put it to use with your iPhone and iPad apps?