If Mike's UBEC won't work for you (it
is kinda big), I've used
this UBEC with good results so far (just the BEC in the link, not the ESC :)). I took off the heatshrink and studied the circuit. The IC it uses is a nice chip and the circuit design is pretty much verbatum from the IC datasheet suggested circuit setup. Very simple circuit too. I put on longer wire and re-heatshrinked it and it has worked great. However, I always use a capacitor on the AUX channel on the RX to help filter any switching noise.
These UBECs appear on eBay from time to time for about $10-$15 shipped. I have seen them at other online stores, but can't recall which at the moment.
Don't get me wrong; I'm not trying to steer business away from Mike, it's just that the Koolflight UBEC is kinda large for such a small vehicle.