Ebay is a good place to look for once fired brass. Last night I was shooting at the range until closing time. I offered to help clean up and while we were cleaning the guys asked if I was a reloader. They told me to pick up as much 45 brass as I could carry.
Buy some off of a local range. Most pf the ranges around here collect all the brass people don't police and sell it to a commercial reloader. Drop by, talk shop with them, and they'll let you have it for a song, if not free.
Unfortunately for me, there is a semi-pro reloader in the area who has struck a deal with the two indoor ranges: he gets the brass, they get a slight additional discount to wholesale price on the ammo he produces and they sell. However, you can recover your own spent cases if you wish.
GunsAmerica has auctions of cases. "The Brass Man" at http://www.brassmanbrass.com/ sells brass that at least sounds good. There is a pretty cheap supply available from www.gibrass.com. There are ads in Shotgun News for .45 brass.
From looking around, I'd say $35/1000 is about the low end for mixed .45 ACP brass. Anyone seen a better deal?
If God didn't want us to own guns, why did He make the 1911?