OSC is the best, but if you have only 2-3 products (less than 20), I do not think you will need such a big one.
You can make simple html pages and can use paypal code, paypal will handle the cart part. That will be the easiest one if you are not good in web programming.
If you are good in web programming like asp / php /perl etc, you can make a simple script of your own. Making a cart script using sessions will be easy. And there are a lot of opensource / free scripts which you can modify according to your needs.
Payment gateway - you can go for Paypal as its simple, easy to use and it is widely used all over the world.