I've probably spent $150 on tools (truing stand, tensiometer, spoke wrenches) and Brandt's book.
I've probably saved at least twice that doing my own wheels, both in savings for replacing broken spokes ($20-35 each and they add up), and catching problems early and fixing them before a break.
It's not hard. The key ingredient to building, rebuilding, or fixing a bike wheel is patience.
Not my problem has become, I'm running out of broken spokes. They're quite handy for stiff/strong wires to have around the house for various projects.