OSCommerce

osCommerce is the leading Open Source online shop e-commerce solution that is available for free under the GNU General Public License. It features a rich set of out-of-the-box online shopping cart functionality that allows store owners to setup, run, and maintain their online stores with minimum effort and with no costs, license fees, or limitations involved.

Requirements:

• Hosting: H250E
• Setup Fee: $25.00
• SSL Certificate: To encrypt the credit card information as it travels over the internet ($65/year)
• Merchant Account and Gateway Account: To verify and charge the credit card (cost varies)

Costs:
Setup Fee: $25.00
Monthly Fee: $19.95 to $24.95/month (includes hosting)