Create facebook app

Hello,
I need to someone to create a facebook app
pretty simple
its an invitation app to my facebook page and it registers points for inviters,
the more they invite, the more points, with a ranking for the top 10

how much would it cost?

we used this script few month again : http://codecanyon.net/item/facebook-viral-contest-application/5229072
you can customize it easily and the support is very good !
and it's cheap


I'm not affiliated to this guy, just happy to work with him