I do want to power one of my Arduinos with a Lithium battery too. My suggestion is to suggested a price for your boards and possible show a general picture of design and dimensions. I think people would be interested in your design if you could give some visual aids.
By the way Itead Studio sells PCBs so cheap that I would just have some made up and build up what you need. Then see if anyone wants to buy your extras. If your design is nice, the board will sell easily.