I believe this cooler would work. It says it maxes at 100 watts, but should work with an additional fan? $10 ea. = $40 per board, $480 for 12.
This ATX PSU is on sale for $25 after rebate. But barring this, you can find a 500 watt PSU for $50 easily, equaling $600 for 12 boards.
Also, Black Arrow prices the chips at $69 each. So does Technobit, valuing 4 chips at €205 = $279. Fire sale prices may be appropriate, but only you can make yourself lose money.