I think you can do it with osCommerce, see the link below for ways to make your cart links SEF: http://www.oscommerce.com/community/contributions,1332
If you are web developer you can get Avactis Shopping Cart for free. As a web developer I applied fro free copy and after 2 hours I got free shopping cart... Also you may look at http://php.resourceindex.com/Complete_Scripts/Shopping_Carts/ . There are a lot of shopping cart with reviews.
That one looks nice, and well structured. Virtuemart is free though, and comparable with the Avactis cart. If I were to spend 199$ on a shopping cart, I would spend it on personalization..