I don't even consider buying new, but I continue to spend a buck a week on the lottery
I haunt regular auto boneyards that permit pulling your own parts. There's ALWAYS something there with work boxes/underbed boxes on it.
I'm not prepared to work miracles recovering something full of holes, although properly redone it would be feasable to reline it with sheetmetal, and use the hole-y box as sort of a frame.
No, I look around, on weekends when I'm not doing anything, there are several boneyards in my area (around Boston MA). Some of the larger yards get up to 100 cars a day.
Flat bed trucks, pickups, all sorts show up. I've been lucky that a lot of trucks of similar age to my '90 F150 have been showing up lately...had to get a power window motor.
The way bone yards are run can differ tremendously from one to another.
One I go to, Rich's Auto Parts in Hudson MA (don't have the number to hand, google it) has numbered rows, and when you ask for a part, they'll print out for you a list of vehicles for you to check. They have their own numbers on each vehicle, and they have good 'inventory' control of their stuff.
They use wrecked buses for parts storage, including some city buses that probably date from the early '50's.
Others are just a jumble of piled wrecks, vaguely divided by brand, type and so on.
BTW, one boneyard, Holland Auto, Treble Cove Road, Billerica MA 800-557-5790 has a sale on the last Saturday of every month, any tire on a steel wheel is $5. I've seen split-rim wheel/tire assemblies that would work on some buses (mostly Budds), both steering and recap tires in good condition.
Woburn Truck Parts, 1095R Main St. Woburn MA 781-933-1546 uses bus frames for holding stacks of rear ends, front ends, you name it. I wandered their yard a few times, looking for stuff for a friend. Pretty good sized yard.
I think I'll post some of this info on the bus boneyards forum page.