First off, given available time, I would rather put in a too many hours and as much money as it would cost to buy retail building a tool, rather than buying factory produced. Where to start on stuff that I have built for my shop? Although my tools work for me, most were inspired by other builders with a few touches of my own. I guess I'll start with my powder coating oven.
My oven was created out of a worn out upright freezer. A lot of people told me not to do it, and in hind sight it would have been easier to build from scratch, but being cheap and liking a challenge, I didn't listen.
The oven uses three elements. I used insulation that I scavenged from old suspended ceiling panels, metal studs, and a lot of scavenged parts. Over all I would save I probably have $250 in the oven at the most. It ain't pretty, but works pretty well.