RetroGaming

Yep, it's the collectors' market. I say that as someone inspired by those very YT channels to get into the hobby myself. But I'm just looking to get games I remember and enjoy, not looking to get whole complete collections or anything. If a game I have my eye on becomes some "holy grail" $500 thing, I can live without it. What helps me, though, is living in a bigger town for a rural area that does have one or two brick-and-mortar retro game stores, where I may be able to find games I'm looking for at below eBay prices. That's another hint; hit up the physical shops you may have near you, be they specialized game shops or even thrift stores. Diamonds in the rough do exist sometimes.

EDIT: I mention rural areas specifically because they usually won't have as much demand driving up prices as the big urban areas will, even if supply is lower.