I've built nearly all the wheels I've ridden in 200,000 miles and have more up and running now than I ever bought. Tools? Park spoke wrenches, a cheap stand from bent flatbar that I paid $30 for long before Al Gore invented the internet. An equally crude dishing tool I modified to not require pulling off the QR or nuts. The big money for a Park tensioner. Relatively recently. Nice for new spoking patterns, For the trusty old ones, I just pinged a good wheel and copied it. Like a previous poster, maybe $150 worth of tools. But half money was spent (on the tensioner) after I built my longest lasting wheelset. Early '80s Mavic GP4s. I rode them until the brake pads wore through the sidewalls, 17,000 miles. I probably tweaked a couple of spokes twice. Built all my racing years wheels with just my bike and a spoke wrench (except one that got trashed by a car. Driver didn't want to ding his insurance so he said "fix it and I'll pay you". Took a half day off my bike shop job, rebuilt it on the work stand and charged him my cost and that half day's pay. He had no issues with that!)
Ben