Try PayPal Express Checkout
The Power Store comparative does say Pay Pal Pro, but if you have a regular PP account, get a signature for PayPal Express Checkout. It is also a free service. The Power Store config. calls for the user email and a sig. This should work.
Also, if you have eCart you can re-configure the cart -- or if you can code at all you should be able to figure it out from the PayPal manuals.
Once you get Power Store hooked up and working you'll love it.