hi, if you have any programming skills (or know a friend who can help you out), that always works out best for specialized functionality. a lot of free carts out there are made to be generic to handle most people, but if you want to start standing out (eg. like special incentive programs for your customers or outside-the-box coupon ideas), you will need to start tweaking the code (or just write your own cart, its really not that hard).
then its just a matter of getting hosting (godaddy even offers free hosting when you buy a domain if you cant afford a monthy cost right now)