i think you should also ask around older people in your neighbourhood or let your friends ask their parents etc. alot of them probably have old cameras at home not being used. got like this many cameras and funny other equipment like old flashes etc. can get those for low price or free if lucky
You can also visit local photo stores where they sell film and ask for expired films to test your cameras, im sure they sell those to you a lot cheaper.
Im using old russian camera Zenit E and i got 3 different lenses for that ^^ rly good camera.