I have website in production where visitors can register for standard and premium memberhsip for free.

Now I need to change it, so when the user populate the registration form and after he click "register now", payment checkout should pop up and after successful transaction I need to save that information to the database.

I need something similar what uskinned.net have when you are going to buy the theme.

Is there something out of the box that I could use for it? I dont need full ecommerce solution.

Any advice is appreciated.

BR