I love this kind of thread! It's what I've enjoyed about the RPF for years now!
Mouse Droid - $50.00 for an RC car from Walmart, body is foam core, circuit boards on sides are foam core with fun foam "chips", and left-over pvc pipe and ball-point pens for greeblies on top. About $65 total.
Leia Blaster from a broken airsoft Beretta, pvc pipe, an old guitar cord, and a flash suppressor I machined out of resin on the lathe. The blaster isn't bent, it's the camera lens. All scrap, so pretty much $0.00
Not really out of nothing, but budget build Yoda saber. Bolsey flash on ebay $29.99, resin yoda saber from the junkyard $14.00 (for the activator and emitter wheel). Grips cut from PVC pipe. Total: About $44.00
Luke ROTJ v2. Machined from left-over aluminum tubing, some copper pipe and a fender washer from home depot, and a pommel from a broken MR FX saber. Clamp is "borrowed" from one of my graflex sabers, new clamp coming from Roman. So really the only cost was the copper pipe from Home Depot and the clamp - so, about $50.
Hoverboard from foam core, plastic bowls and plates from the dollar store, and leftover styrene from my R2 build. Printed the graphics on my home printer. Cost - about $20.00. A few build pics -
http://jedi5150.com/gallery/thumbnails.php?album=22