We had an old barn that we wanted to tear down until dh wanted to get some hens.
Well, we fixed it up and used a corner of it for the coop. It was about 4 pieces of plywood ( untreated cheap stuff ) which was under 30 bucks for hardware and plywood.
We used an old shelving unit and converted it to a 6 hole nesting box. We bought 6 Buff Orp hens that were already laying but the silly things wanted this one corner to lay in.... and it was causing a ruckus lol so i put a plastic milk crate in that corner and that is their favorite place to lay..... we already had the shelfing unit and the milk crate so those were free !
We cut out a hole in the end of the building for their entrance/exit door and we already had extra kennel fence panels from my labs so we used those.
I just bought 21 chicks and one died so I'm down to 20. I got most of them for 1.99 at TSC and Rural King and a couple of them for 1.49 so that was cheap ... bag of 50 pound feed was 10.50.
We bought the waterer and feeder for the older girls and those were in thr 20-30 dollar range for each. We bought a heat lamp but didnt use it on the big girls aka my hooligans. That was about 10 bucks including the 250 watt bulb.
We also bought some "chicken wire" and I have no clue how much those rolls were as hubby bought those when I wasnt with him.
We've used a lot of them for different things so all of that cost cannot be attributed to the chickens.
We also built another small coop and between using what we had, the hardware, the lumber etc , we have about 200 bucks in that.
We also recently bought two more dog kennels from a friend for 50 bucks each. A major STEAL ! to extend the girls yard.
You can look for things you might need at yard sales, on Craigslist, on Freecycle groups ( in your county and surrounding counties ) and out of the 2nd's pile at your local home depot, menards, lowes etc.
We did one thing at a time.. we worked all last summer on fixing up our small barn and by fall we had gotten our 6 buff orp hooligans ( they crack me UP lol ).
So really, the bottom line is that you can go as cheap or as expensive as you want.... remember... the chickens do not care what their home looks like as long as they have shelter, food, water , a place to lay their eggs and a place to be in the yard to peck for bugs and grass .....
Best of luck .