I'll order bare prototype boards today. When they arrive (in a few weeks) I'll build a couple for testing and, if there are no significant changes needed, will get quotes on assembled boards. Once I know the cost, I'll need to gauge how many are interested before placing an order or abandoning the idea.
The added hardware in the picture below are a 50-ohm BNC connector (for an antenna) and two 3.5mm stereo sockets (for serial ports).