scounge! start reading Craigs List free section, if you live in an urban area, drive through around garbage day (old doors, windows, etc free for the taking).
tell everyone you know you are building and need wood, shingles, wire, tools, etc -
consider deconstructing pallets (do a byc search and an internet search) - free wood, a pain to work with though, but...free
be creative - can you reuse a playhouse, shed, lean-to, dog house, etc.
what part of the country are you in? In the south you can get by with less, in the north you need more....
sorry, but 250 wouldn't go far enough to build a very small coop here in Minnesota A couple of years back I built a coop that would house a dozen at best, spent about $500 on wood, scrounged the doors, shingles, windows, hinges, hasps, etc.
good luck!