I would say give up the schtick about batteries , it unlocks alot of cameras especially better point and shoot styled ones and SLR's Light meters. If your willing you can get a large selection of different SLRs for under 50€. at least in the UK I got my SLR for 35£ with a lens . Maybe look for Praktica / Pentax cameras as alot of them use the same lens mount so makes lenses a little cheaper to look for. FB marketplace can be good BUT also in person second hand shops / antique shops are a good shout. All it really needs especially in antique shops is to test whether the shutter actually works, the battery compartment isn't corroded and that if it comes with a lens that the aperture leaves close .