Have you considered an Analogue Pocket? It's like an "upgraded Game Boy" with a better screen that can also play games from the Game Gear, Neo Geo, etc.
Nice device, but for $290 it should last longer IMHO.
And if I am going to emulate I might as well get them an Anbernic or Miyoo emulation device. But, those can have complex and annoying user interfaces. I guess it could work and I could make SD cards that just have a handful of games.