I want to integrate paypal payments pro with my site.

I use a custom made scrit as a shopping cart.

I need the script to accept payments by CC on my site and express check out to work.
If payment was valid - customer needs to be forwarded to a order sent page. and update a field in my db with status of order.

Paypal has a very good example file of what i need to their forum, I just need a little bit of help to make it work with my site.

I don't have a big budget. How much would you charge for this?