This is asked from time to time, and you should find a few threads
in the archives

> a) use a very low power 5V regulator which is comparable expensive.

What do you call expensive ? Seiko, Linear, and National all do
ranges of low power LDO regulators. As many (including me) have
found though, you may have to buy fairly large quantities to get a
decent price

If you've got a few to make, then a circuit that requires much more
assembly than a simple regulator may cost more in labour

What is your "12V" ? Is it true 12V or a nominal 12V (perhaps 13.8V).
LP/LDO regs don't always like > actual 12V

> Is there a third possibility i dont think of?  I feel that from the two
> mentioned either has its drawbacks in a low cost radio control?

I use the LP2951, which can be turned on/off by a single pin. I also
use Seiko LDO regs when I can get them, and Seiko S81250 to
replace 78L05. How much transmitting power do you need ?

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