I wasn’t really suggesting a group buy, but I guess that’s kind of an obvious way for it to go. There are at least three different Chinese companies (itead, seeed, and elecrow) offering PCB fab services in lots of 10 boards, often cheaper than you’d pay for a single board stateside. And for whatever reason, 5 x 10 cm is almost the same price as 10 x 10 cm with all of them. If we didn’t need a gold finish, the price per board could be just over $1.
Just to be clear, I’m not volunteering to coordinate a group buy. The board size would need to be reduced by at least 6 mm on the long dimension (the price increases significantly if it’s over 10 cm), and while I might feel comfortable tinkering with a simple, low-frequency design, I honestly have no idea what if any effect that would have on this design. I’m quite sure it can be done; I just don’t have the knowledge/skill to be comfortable doing it. I also don’t have access to any tools to cut the boards apart at the moment.
The rest of the parts look like they would be very inexpensive–the SMA connectors would be the most expensive by far, at $3.25 ea.; the remainder of the parts would total less than $1.