You may have 10 products or 1,000, but the result must be the same... to take orders over the web. You could purchase an expensive shopping cart system.. but don't have to. There are a number of free, Open Source, carts on the market. By using them you have the advantage of being able to customize them to your needs without licensing restrictions and you save money.

CommerceSQL is a more lightweight shopping cart system. If you don't need a cart with a full templating system and the other features of Interchange, this one could be the one for you. It's quick to install, configure and easy to run.

This is one of many cart systems, but I feel these two can meet the needs of most people who want to start an online store.