Need Simple Paypal Payments Gateway 2

I need a simple Paypal payments gateway like shown in this site:

There must be dropdown list menu with price options.
User will pick one
Ater user picks price options, script will calculate 50% for buyer to pay.
User will click checkout button
User will get redirected to paypal to pay, then come back to website.

I need this simple system done now, only bid if you can do.

Thanks.
GFD