Planted Tank Guru
Join Date: Mar 2010
Location: Sacramento CA area
When it comes to e-commerce, I wouldn't risk any of the "free" themes out there unless they use paypal as their only means of payment.
Judging from your site, you have experience with using paypal carts, so you could always do that as well.
You also have the other option of using godaddy hosting and e-commerce as well. It would cost you roughly $20 dollars a month for the hosting and shopping cart. The shopping cart is pretty darn nice and user friendly the last time I researched it. It even shows customers updated quantity information if I remember correctly.