Good luck finding an old flip phone that still works properly - I have a modern one and it only cost me about $25 for the initial hardware, and $40 every three months or so to keep it running (unlimited talk and text, no data). I went to Walmart, they keep them locked up because they're almost exclusively used by drug dealers. The markets for working old electronics have been ruined by speculators - much of the market is just resellers buying from each other to try and make a profit - there's very little in the way of actual enthusiasts and collectors - at least in my experience.