I just sold a psr 950 for $500.
I think an older model would be fine too.
Also, those psr ā eā models cost less $300 new, and I think would be perfectly fine for what you need.
I have a psr e 463, and it sounds pretty darn good.
https://www.guitarcenter.com/Yamaha/PSR-...ASABEgI2PvD_BwE