Our city has two used places with really really cheap lumber, windows, doors, etc. One's the Rebuilding Center and the other is the Habitat for Humanity store. We got most of our lumber as salvaged scrap from a housing complex, amazing what they toss, but the windows, doors and other fixtures came from the Rebuilding center. A lot of the nails that went into assembling it were salvaged from building our own house.
The gates to the run are actually heavy duty steel mesh doors from a high voltage utility vault. No durn coon will get through them!
My portable coop was torn up 2x4's I got for $1 a piece off a lumberyards salvage pile. The second level is a dogloo my husband found in a garbage strewn lot. We call it the penthouse.
Paint is always ultra cheap mismixes, that's why my main coop is purple.
I admit to dropped $100 on the current coop I'm building. But it's going to be visible from the street so I want something that looks real nice. That doesn't mean there's not salvage involved. It will have 4 wonderful old windows I pulled out of a dumpster. Broke my hear to see the wonderful french doors they'd already thrown concrete on and smashed. The roof is being waterproofed with pieces of pondliner left over from putting our pond in a few years ago.
See, lots of salvage out there if you keep your eyes open.