The ones you can find online are sold by people who know the market all too well so the prices are high. Plus it's online so there's no guarantee about anything.

Pawn shops, thrift stores, or their "modern" equivalents (EasyCash, CashConverters, etc. YMMV) would be a good start. I got mine out of a pile for 10€ at a countryside GiFi (French store) ten years ago.