LE33CZ-TR voltage regulator, and two capacitors. We are using a 12v nominal input, but this circuit will handle up to 18v input (for when the house batteries are charging at 14.4 or so, and the occasional 15v equalize).
497-4258-1-ND (LE33CZ-TR 3.3v Regulator) $0.88
BC1148CT-ND (.1 mf 25v ceramic cap) $0.44
445-2866-ND (2.2 mf 25v ceramic cap) $0.26
I will be building a 5v regulator soon as well with the same input requirements, using the LE50CZ-TR 5v regulator, but Digikey did not stock this part at the moment. The inhibit circuit shown does not exist in the 3 leg TO-92 package, only in the surface mount 8 pin SO-8.