Bitd one of my workmates decided to see how cheaply he could build a decent bike for. He managed to do it for £10 and that was using a Cannondale frame he found at the dump. It had a snapped chainstay and the paint was flaking off (like they used to). He had the frame re-welded and polished up which was the £10 cost. Everything else he got out of the bin. Took him about a year to do, but he managed it!
I bumped in to him the other day and asked him about the bike and he said he's still got it!