Simple cart (but low budget)

[dhtml12345]

I don't believe there is a module that integrates with PayPal Pro, though it would be great to have one.  I might contribute several hundred dollars to see it done.

[cyberman]

There are some several Paypal solutions (in development) - not sure if they do what you want ...

http://dev.cmsmadesimple.org/projects/feupaypal/
http://dev.cmsmadesimple.org/projects/paypalgateway/
http://dev.cmsmadesimple.org/projects/checkout/