Try getting paid for ur app using ads instead. Making it free this way for the users would be a win-win situation for all. I don't know if this is possible on iPhone and iPad apps or not, but thats how some jar games on my Nokia phone work, so I'm guessing that should be an option for you too. You could post on your app's website (if u've any) that any interested advertisers can contact you if they wish to advertise using ur app :-)