Great news! ArduPilot is now available to buy at Sparkfun. The price is $24.95 (or buy 100 at $19.96 each ;-)). Note: there is a limited number available now, but Sparkfun can make more pretty quickly so get your order in now and they'll be filled from backorder in the order they were received.
Huge thanks to Nathan Siedle at Sparkfun for helping us get through the production snafus and otherwise taking this project under his wing. Now let's win his autonomous vehicle competition with an ArduPilot-guided plane!