PCB assembly cost per-board
I went and got online quotes from two assembly houses for a simple board with 60 surface mount components (all on one side), no fine-pitch, bga, through-hole parts or connectors, and lead-free processing.  Medium delivery time, neither rush or extended.

I then requested quotes for 1, 2, 5, 10, 20, 50, 100, 200 and 500 boards.  Only the second house would quote over 100 boards online.  Then I plopped the #'s into Excel.

Here are the prices (in $) per PCB for various quantities for the first assembly house:



and here are the numbers for the second house:



The actual figures range from $318 for one board down to $11 / board for 100 boards for the first house, and $448 for one board down to $16 / board for 500 boards for the second house.  Guess which one is based in China.

What I find interesting, is although the prices are quite different, the shape of the two curves is almost identical.  Prices rise from their lowest point until they double at around 20 boards, and in both cases there is a very sharp knee right at 5 boards.  I had thought the knee would be much further right, i.e. having to pay a steep premium for even quantities of 10 or 15 boards, but I guess that isn't the case.