eCommerce store design, implementation, direct integration with eBay

Design is basic L shape: header, left nav, main content section highlighting key products. Preferred colors, a basic logo and examples to be provided.

Implementation is currently on Go Daddy, but will be moved to a more robust eCommerce solution. Prefer to use 3DCart or Volusion, but I would like your recommendations as well. Please indicate what solution you would prefer to work with.

Client would like to manage their inventory via the eCommerce solution, but allow immediate upload to eBay as well. Some eCommerce solutions have add-ons that allow for this, but an expert in eBay APIs should be able to develop one easily as well.

Looking for a 20-day turnaround.