Compare to "Free" Carts
"Free" shopping cart solutions seem like good idea until you realize that any meaningful functionality comes with substantial costs. If you search through contractor websites like oDesk or Elance, you will see these sites are filled with requests by website owners who need help with these "free systems": design/integration isn't easy, certain "modules" like PayPal or Authorize.Net don't work, shipping integration isn't working, etc.

The free systems may sound good in theory, but you'll be forced to learn the more techical parts of web design, and you'll be searching for hours through forums, as almost none of these offer actual technical support.

The chart below shows a leading "free" cart that is quite expensive if you want it to do anything.
NeuCart WooCommerce
Advertised Cost $85(a) "Free"
Product Management
Product Options (size, color, etc) Included $49/year
Import Products Included $199/year
Add product to your cart via URL Included $49/year
Google Product Feed Included $79/year
Customer Experience
Customers always see shopping cart Included $79/year
Product Search Included $79/year
Pre-order products that aren't available yet Included $129/year
Play Audio Samples Included $29/year
Shipping and Digital Delivery
UPS Integration Included $79/year
USPS Integration Included $79/year
Per-Product Shipping Costs Included $79/year
Canada Post Shipping Costs Included $79/year
Digital Product Delivery with PDF Watermark Included Not Supported
Custom Shipping Rules Configurable $199/year
Payments and Checkout
PayPal Included Included
PayPal Express Included $79/year
PayPal Pro Credit Cards Included $79/year
Authorize.Net Credit Cards Included $79/year
Stripe.com Credit Cards Included $79/year
In-Person Payments Included Not Supported
Coupons Included $99/year
Advanced Coupons(b) Included Not Supported
Sequential Order Numbers Included $49/year
(a)Advertised Cost refers to the self-installed price of $85. The hosted versions are $10/month or $12/month for the hosted version with SSL, which is required if you are accepting credit cards directly from your store.
(b)Advanced Coupons refers to coupon configurations like "buy one get one free", "shipping is free with $50 purchase", "buy three CDs and get 50% off two songbooks", etc.