There are much simpler/cheaper options on eBay for "buck" voltage convertors. Usually just a dollar or two, and they'll handle anything from 60V down to 2V over your output. No heat to speak of, even when stepping down from outrageously large inputs.

Eg. This one for a buck, delivered (slowly). Or pay a bit more on dx.com and get it within a couple of days (yes, they now have FAST delivery on a lot of stuff).

For this application, even a 7805 would actually work just fine without too much heat, because the current draw is likely to be in the milli-amps range. I have built several devices here that take 12V in through a 5V linear regulator without much fuss. I do put a small heatsink on some of them, but not all.

Cheers