The sky is the limit! In all honesty, if you are trying to go cheap, scavenge as many materials as you can first, free on craigslist, or construction sites, etc., then plan around it and figure out what you still need to buy. I think my biggest expenses were the roll of welded fencing I bought (due to predators I needed to thoroughly fence all sides and top), and then nails/screws/fence staples/hinges/latches etc. I came in around $300 for my coop plus run for a slightly smaller flock. Even when I kept adding on, it still ended up being waaaaay cheaper than anything pre-fab of similar size. I probably need another gallon of paint and some roof shingles (which I'm hoping to score from a job site) so maybe another $50. I gave myself a budget to start and did what I could to stick to it. I was able to make it "chicken ready" within budget, and now when pay day rolls around I sometimes splurge on extras. Next I'm buying a new/different latch/lock for my gate to make it more secure. Remember the chickens don't care what it looks like inside but your neighbors might care what it looks like outside.