As a point of reference, for one of the companies I consult for, they do their own custom hardware for industrial automation.

The BOM of that board is about $70. The landed price in the US (after PCB manufacture, Assembly, Shipping, and Import Fees) is $130. These are done in quantities of 100-200 per run....if they do a "prototyping run" of 10 boards, the cost comes in at about $240 per board.

I'd be willing to bet its very difficult to do a single board for less than say $250 once every thing is added up.