My suggestion with you is to go with OSCOMMERCE... but before I point
you in that direction, can you be more specific as to what you will be
selling, the quantity of items?
See here is my thing, if you`re going to sell less than 50 products, it
would be better to go with a simple cart that can handle just that..
perhaps, a small-shopping cart system.
If you`re going to sell more than 51-200 or 500 products, go with
OSCommerce, Os Commerce gives you, a checkout system,
pay pal and Credit Card Processor Integration. UPS, USPS, and FED EX
shipping Modules, that calculates everything for you. It also has a
Login, for returning customers.
I think your solution would be to go wit OSCOMMERCE
Web Developer / Owner / Consultant
When starting your own business the need to "know-how" is greater than money!