It sounds like you are in Europe. Not sure if there is a parallel, but in the US Craigslist is an audio bargain hunters dream. Many people are dumping old audio gear, and decent stereo receivers and AVRs can be had for “pennies on the dollar”.
I’ve picked up a number of perfectly functional used receivers for under $50, and a handful of those were $0-10!
Until proven otherwise, all compently designed amps, in functional condition, operated under clipping, are indistinguishable. (This is not how it seems to me, but the results of careful ABX testing have not been refuted AFAIN)
The downside of used is reliability. I like finding “good deals” on people unloading old audio gear. What can often be the case though is that gear has been sitting unused. The last time the seller listened it was working, but that might be years ago. So you if you don’t want a dead unit, you have to check that it’s working.
Another downside is size and aesthetics.
But I listen to an old Yamaha AVR I got for free everyday and it sounds just fine. It also has a built in DAC, multiple inputs, surround sound capabilities, and six analog inputs to its six amps, which is interesting for experimenting.
I mean it has a remote, it has A and B speaker outputs, and I think each amp is rated to 80w.
It’s crazy.
Stereo amps from the 90s are a good bet, Sony, Denon, Yamaha. These have no cache with vintage fanatics, so around here you can barely give them away.