By popular demand, ArduPilot Mega is now available as an all-in-one kit for $250. It includes everything you need for a functioning autopilot with GPS, even including RC cables.
We'll soon be offering wireless telemetry options for this, too, along with a ArduCopter version that comes with a magnetometer. A pre-soldered version of APM will also be available in a month or so, once we put in place a rock-solid testing process.
In the meantime, you can buy APM pre-soldered with code loaded and tested from uDrones for $349.