It took about two months, but that was working only about one day a week.
All the racks, and the controllers, and the steel for the bottom are from a local junkyard. I've got at most $200 in it, and the bulk of that money was for stuff I bought new - paint, JB Weld, and the heater coils. I'm sure we've spent much more than that for brisket!
It was a really fun project, and I'd help anyone do another. You could easily make one from scratch, I'm sure.