I picked up a rail-straight western red cedar fencerail at Lowes a few years ago and decided to fool around with it. I made an English longbow with a full bend thru handle design, 77" tip to tip. I started 1 1/4 inch wide at the handle and all the appropriate 5/8 rule futzy stuff and ended up with about 30 lbs of draw weight and 6 inches of set on the most perfectly fretted piece of crap you ever saw! The sapwood to heartwood ratio on the finished product was a lovely 1:3 ratio. I left a string on it and hung it in the garage, pretty as a picture, absolutely no cast, laughable effort at best.
Materials: $6
Time: 3 hours
Value: Poops and giggles.
Blackhawk makes some good points, make sure you know the species of wood, know for sure that it was handled properly air cured, vs laying on the ground picking up mold and rot, etc.