I import items and sell them on a site called TradeMe (similar to eBay). I want to create a website where I can also sell items. I already have a script that manages all my stock and listings for me but I need an ecommerce script that I could easily modify to implement my stock management script into (so when someone buys something off of TradeMe, the stock goes away from the site).

What script would you suggest I build my website on bearing in mind my requirements?