>>1827024I buy parts in job lots, off people clearing them well below cost, salvage them from dumps and buy whole fucked bikes to salvage parts from.
It's a misconception that you even need parts though. People who don't have lots of bikes and a huge parts bin already should pick higher end projects that are complete and do not need parts. The only common thing old complete bikes might need is wheels.
The things you need to have a really fresh old bike and do a complete overhaul are consumables, buying tires, tubes, chain, bottom bracket, cassette, cables, grips, pedals. That stuff adds up, it's ~$100-$200 to do a bike. All those things are readily available new and are just best bought new online.
Custom builds are vanity or the realm of true bike hoarders like myself.