I found a listing for a Denon AVR-X2600H including original box along with speakers (4 ProMonitor 80 satellites, ProCenter 100, and ProSub woofer) and wire for $380. It seems like a reasonable deal, although I haven’t looked up the speakers. We moved several years ago and now have a bonus room that I’ve always intended to be our home theater but currently has an older 4K TV (only 1 4K HDMI input, not HDR) and soundbar with wireless subwoofer from our old house where the TV was in an open living room. It’s never been in the budget to upgrade, and I’m not actually sure I could spend this because we had some unexpected expenses recently, but it’s certainly a more budget-friendly way to go. I think it would be a decent setup and upgrade for our current equipment, but I’ve never bought a surround system before, especially not used.
Have you bought used before? Any concerns with that in general or this system in particular? If we ever upgrade the TV to a newer 4K/HDR the receiver might be missing some features that would be nice to have, but I have no plans to do that unless the TV actually dies which hopefully won’t be any time soon.

I’ve bought and sold my fair share of used gear. I view it as a low risk game - as long as you know what you’re looking at and can adequately test it you’ll save some $$. If you change your mind in a few months or years you can always sell it again with much worry.