I’m focused on NES, SNES, N64, Master System, and Genesis at the moment. I’ve just about reached the end of the cheap NES games and bought an Everdrive N8 Pro earlier this year. Mainly for ROM translations and homebrew, but I will admit to playing some of the higher dollar games on it. I’d much rather play actual carts though.
For me personally, I’ve found that I’ll go upwards of $60+ for a RPG or meatier action adventure game, but haven’t so far spent more than that on any of the consoles.
I’ve also opted to buy ports over original games in some cases. Chrono Trigger for example, I won’t spend $250 on it so I bought the Japanese DS port since it was $30 shipped and supports English out of the box.
It would really depend on the individual game itself as to what I would pay, but I suppose if I had to give a hard upper price limit, I would probably say $100. Don’t care what the game is, I’m not spending triple digits on it, old or new.