You might want to consider this:
http://www.moderndevice.com/RBBB_revB.shtml
It doesn't have a USB interface but you can add one with this:
http://www.moderndevice.com/connect.shtml
One USB interface is all you will need for multiple RBBBs - you could develop and put your project into the RBBB and just get another RBBB for the next project if you don't want to reuse the first one.
Another benefit is the RBBB will plug into a standard prototype board. I developed a rather large project this way and found it a great way to go.
And the price is certainly right. And yes, it will do everything the Duemilanove will do.