Help picking a shopping cart plugin

I need help picking a plugin for my site. I’m a novice and only just recently figured out what plugins can do for me!
The site I maintain is for a continuing ed seminar company. The site is used to give info about the current seminar being offered and to provide online registration. I think what I need is a shopping cart plugin, but maybe there is something else that would work better. Currently, I have registrants fill out a form (cformsII)in which I get all their contact info (which is then added to an Access database by hand) then they are redirected to a page outside WP that allows them to make seminar selections that go to Paypal for payment. I created that page in html using PayPal button code. When they check out with Paypal, they have to re-enter all the contact info that they entered in the first form. Surely there is a better way! Ideally, I’d like something that would be in WP, not have participants entering everything twice, give me the info in a format I could dump unto Access, work with Paypal, and allow both percent and fixed dollar discounts. Too much to ask? I don’t know. The site is http://www.crnaseminars.com but I have the registration part down right now while I work on it. I’ve tried out several free plugins, but they’ve been too complicated or don’t do quite what I need. The closest I came was with “WP Simple Paypal Shopping cart” but it does not have a fixed dollar coupon option or a way to capture the participant info so they don’t have to enter it again in PayPal. Any advice?