TI has two parts that are in the $4 range ( singles ).
They are switching regulators ( buck ) with built in FET switches , 4.5V to=
 18V.
TPS544B20 and TPS544C20
There is a modeling tool , eval board ( $50 ) , samples =85
http://www.ti.com/product/TPS544B20

I think even I could figure this out.=20
Gus in NW Denver=20
--=20
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