Roughly how much do programmers change to create Apps for iPhone/iPad? Does the client get the coding?

I have seen ads in magazines for companies that say they will take your idea and make it into an app.

I am slowly learning how to create apps and was wondering if anyone knows how much these companies charge?

If it is within reason I may go for it,

Also- who owns the coding?
If it is for reference could I use it again for a second app with a new topic? Would I have to pay again?

Please let me know anything helpful you might know on such programmers as well.

Thanks!