It only going to get worse.
In the 90s, I used to get "retro" games for under $5 a piece, regardless of what it was, because no one cared about "crappy old games".
In the 2000s, people started to care, but the scalpers and resellers still weren't keen on it. So while it wasn't an under $5 market, it was still manageable with most retro games being under $20.
Nowadays, even shitty games are $30 bucks are more if it's anything other than Sega Genesis or Atari 2600. It's getting to the point where it's not even fun anymore. I've pretty much moved on to seeking out comics, DVDs, and VHS on my local hunts anymore. eBay is the only reliable way anymore, and even then it's not cheap.
Thankfully, I got most of my first party titles (especially Nintendo titles) before this got completely out of control.