Customized Ecommerce

I need a very simple ecommerce web site, but a little different from the actual stores.

It is a service ecommerce, where the pricing will depend on the customer.
The customer will send to me an invoive and that I will pay for and charge commission over it.

The invoice could be sent thru attachment from the website or it could be issued by the customer typing the barcode on the proper bank website.

For that I would include the online payment methods availabe in Brazil, like Bcash, pagseguro, moip.

Need a clean and simple website and need a quick development as I think is is not complicated.