Well, this morning I was looking around online at other people's homemade mills. Many people built theirs from scratch, but I have discovered another community of people who have purchaced regular manually operated mills and retrofitted them to be computer controlled. Since there's nowhere in this town to build the needed parts to build my own machine, I figure this is the route for me.
Looking around online, there's a Harbor Freight in Bakersfield, and they have a mini-mill in stock.
Well, I'm back from Bakersfield, and I have a new mill.
The mill came in a crate, which I neglected to photograph. It looks like it should be pretty easy to modify to use stepper motors to move the X Y table. The Z axis will be a bit more involved, but should be quite do-able.
While I was at Harbor Freight, I also picked up some high-speed carbide drill bits. They should be fine enough to use for circuit board work.