You know, it is funny. I hear so much about how unreliable vintage gear is, but the majority of problems I find is crackly controls, one side that is out, or blown fuses. I fix the majority of what I get myself, and most of the time, deoxit or a replacement fuse fixes them up. I clean all the dust out of the unit, clean the cabinet, front panel, and knobs, and they look 8/10 or higher! You just have to be smart about what you pick. Make sure it works, and no bizarre problem that jumps out at you as not being fixed by a good cleaning, deoxit, and fuses. A person should be able to get decent sound for under $100 if you aren’t picky about cosmetics. And then, you can upgrade components as your interest grows. You should be able to get a good sounding setup if you shop carefully for about $250! At $400 and up, you should be able to get great sound. Pick good reliable speakers with rubber surrounds, unknown name brands that you can hear, but sell for much lower prices of the brand name. Sears, MCS, older Lafayette, Yamaha, Kenwood, Sony, Tamon, Speakers made locally using quality components, Realistic, Radio Shack, Hitachi, Toshiba, Nikko, Sharp, Fisher, especially mid 80s and newer! This is great entry level gear that won’t cause you to shed tears when it fails. Just beware of gear affected by those failure prone caps from the 90s. Easy fix if you are handy and you got it for free.
I have turned on many kids to stereo systems, and I saw many younger people last year when I was selling a collection. I am constantly surprised at their knowledge of music from my years. And there are a bunch that are into boom boxes! Imagine the cool factor of making their own tapes from a decent vintage system! (Edited) For cassette decks, I would recommend a newer Denon or Yamaha deck.