If you use the OScommerce and 2checkout option, the costs are very clear and you will find very affordable.

First, there is the cost of the hosting account type you choose with us. Next comes the OScommerce software which is free with any Linux hosting account of level Ultra-LT or higher. Last is your payment gateway fees. Signing up with 2checkout costs $49 setup and $0 monthly. You also need to account for transaction fees every time someone buys something. Besides that there should not be any other fees, unless of course you sign up or with or use a different payment gateway processor.