Everyone has app ideas, you can't mention being an iPhone developer without some one giving you an app idea they have. 30k is a number that weeds out the people who don't really believe in their idea. It doesn't take much work to come up with an app idea but it takes work to make it a reality, probably more work than you realize. The person doing all the work to make the app isn't going to charge a few thousand and let you run away with all the money if it's as successful as you believe it will be.