Wp-e-commerce is free, but you will likely want to upgrade to the gold cart option which is rather expensive. I've found it to be a really good shopping cart plugin for WordPress except for one thing, the SEO optimization sucks, really bad. Just recently were you able to make titles match the category and product names and that is the best they've done yet. Everything else is seriously lacking. No title, description, or keyword customization for individual pages like categories and products. They use the homepage's keywords, description and title which can really hurt your rankings. Anyone else used it? So far it looks promising if they can do a big update for the SEO side of things.
I would really like to get some feed back from those who have used Wp-ecommerce, I have been contemplating on WP-ecommerce and I have heard that its a pretty good shopping cart. Never got any feedback on the effectiveness in rankings or may be seen a thread that talks about it.
I used it for a couple of months a year ago and ended up switching to zen-cart. It just doesn't function properly and makes every little thing a chore. If you are only selling a product or two then go for it, but if yours is a full e commerce site then get a real shopping cart.
i have it running on my site http://game-script.net customized with new layout and images. However i find it hard to now get the pro version even if i wanted to get it as things changed in certain pages already customized. + looking for an alertpay option for the cart.