Check out my BYC page... I used alot of stuff I already had in mine and then my dad's sheds and items I found cheap and salvaged.
Also PVC pipe or Rebar (the small thin kind - but its runs a bit more tha PVC) make good run frames.
Ask around, post ads on craigslist your local radio station anything looking for people who are remodeling their houses or business and see if you can't salvaged their scrap left overs or the materials they would otherwise dump...or need a building torn down and offer your servies to help tear it down if you get to have your choice of the stripped materials.
I was lucky and happened to stop and ask these guys working on their mom's roof if I could have at the old materials, had gotten some good decent shingles but wound up not using them, but they got my # and called me back when they finished and sold me the new whole pieces and a scrap piece of plyboard they had left over for a bargain. Its the exterior kind of plyboard 1/2 inch which runs about 30 $ a sheet and they sold to me for 15$ for all they had left I think.
Just looking around, freecycle, craigslist, local radio station, newspaper, etc for materials....Milk crates for nest boxes (you can tend to find those free at alot of places) pallets - many places just toss 'em out and will let you come get what you want, flea markets or the re-store. Shop your hardware/improvement stores for clearance items or scraps (I hear of alot of places will sell small sections of tile, vinyl, and carpet thats left over from their rolls/boxes for WAY cheap - a couple cents per sq. ft)
The possibilites are endless!!!!!!
