These ads are usually distracting, and too often can be terribly annoying. So while you do get to save on a monthly webspace rental, you may very well be losing most of your customers. Really, not a very good deal. T-3 access to the Internet for all their connections. As with any agreement, read the fine print, and don't sign on longterm until you are assured they are dependable in every way.
All prices are per month.
They do not host your site, just your shopping cart, so you'll still have the per month hosting charge somewhere else. While this is a serious committment, there are some reasons to buy the software - in particular, the flexibility to configure it the way you want, a seamless interface with your website, and the opportunity to add a considerable number of items for sale. Many of these carts will also have database integration.