Customize a Wordpress Theme!

The task is very straight forward: We want you to take this theme and make it so that USERS can register and publish their own Music. The theme allows the ADMIN to do this already. But we also need users to be able to set prices for each song and we need to collect the sales. I asked the AUTHOR about this and he said the following: "Hi, it’s possible but only through WP Admin interface (you can set Contributor role to new users). Also i’ve seen a site on Replay with Gravity Forms plugin used to add content through the front-end." He suggested I hire a Wordpress coder so that is why we opened this project. Here is the Theme, we have not purchased it yet but I have a copy of an older version.: [login to view URL] We do not want to change anything else about the Theme. Please outline your approach and price. Thanks! Daniel