I would second that if your only doing it to save money.
I bought an old raing bike from the tip fot £5 a few weeks ago to make in to a fixed gear. It is going well and should be brillient when finished but so far I have spent about £90 on it mainly because I am building a new rear wheel for it but I expect to have to spend a little more on a few other bits and bobs. However I do like getting old bikes and doing them up just for fun but it dose not make a profit. I recently got a mtb off of freecycle for my girlfriend, spent a day cleaning it greasing and rebuilding it but it turned out to be a tad too big for her. Still I can sell it but I would only get about £30 - 40 for it, not exactly a good days wadges but I still enjoyed my self taking it to bits.