[blister]

We used a shop exactly like you described: http://www.e3embedded.com/

We used them to design and build a custom board for our Sumo robots that had our V1 built from an Arduino board and a custom board that plugged into the Arduino. We couldn't really afford to pay them a big chunk up front, but we negotiated a pretty pleasant royalty deal that comes out to a few dollars per board (which we get manufactured for less than $10/board).

They did excellent work and I highly recommend them for that type of "prototype -> production" path.