I finished building up another bike last night, a Gitane fixie (fixies are like single speeds but without freewheels; the rear cog is attatched directly to the rear wheel, so whenever the pedals turn, the wheel turns, and vice-versa, makes riding quite a bit different). For about $20 ($15 for a rear cog and $5 for a new tube) I managed to scrounge and fashion myself a beautiful bike.