Battery not charging, no battery indicator light.

[alm001]

I've had a problem over the last two weeks that I initially thought was my battery.
The car started to crank slowly one day, but it drove fine. The next morning it also cranked slowly so I relegated myself to buying a new battery, and drove it to work anyway. Started (slowly) for the ride home, but I stopped at the bank after the 20min ride home. Leaving the bank - stone dead. I charged it over the weekend, and the battery held 12.7+v in the garage. I drove it Tuesday and it seemed normal. I went to start it today and it cranked slowly again. I popped the cover, and put a meter on the terminals and it was showing 12.5v with the car running at idle. I didn't bother the wife with revving it up to check, and I just parked the car to deal with later. Never had a battery light come on.

If we can assume that alternator/regulator is bad, I have options;
-Get a whole alt ~$220 with a new belt
-Get a voltage regulator ~$40 (90 with a new belt)
-Get a voltage regulator and do an underdrive pulley while I'm in there. (Comes with new belt) ~$220 total

Any more tests I should run? What are the chances I change the regulator and the whole thing is bad?

Has anyone used the "Synamas Products Group" UD pulley from ebay?