Here are the stores I have been referring to.

1. - I built this for Gower Enterprises using html (and got a pro-designer to redo it when it started making some money) and added shopping functionality using Roman Cart.

I really, really recommend Roman Cart as a solution to quickly make an existing website into an e-commerce website. However, they don't have the flexibility of BigCommerce. I don't know how easy it is to integrate BigCommerce with an existing website.

2. - originally an OS Commerce site, we had it rebuilt as a custom solution. Cost us a lot of money when things went wrong! (Now all fixed, though!) This is my least favourite solution.

3. - This is the store we have set up with BigCommerce. If we haven't updated it since I wrote this, it is with the default template, which I think looks the best of the options.