I was able to build my coop for over a dozen bantams for under $50 in 2x4s and hardware. The rest was recycled from garden center shipping pallets that utilize lots of longer wood and flat sheet boards to stack full sized pallets onto each other like shelves. I didn’t use any actual pallets beyond the base of the coop because of how difficult I found tearing them apart, but I could have had even more wood if I’d put forth that effort. If you ask around your local businesses l, you might strike gold— or free wood rather.
I’m not the most constructive savvy, but it was easy to build a basic 4x8 box with a single slope roof once I had enough free material to learn and make mistakes with.
Any prefab I was looking at would have easily run $100s of dollars for the cheap stuff, up to $1800 for some of the better built coops or even a used shed in these parts.