I agree, that CM3 is one of the the best solution for a performant portable retro-gaming system (apart from mobile phones with snapdragon processors, but they are a bit more expensive and you are limited to emulators for android and can not use Batocera Linux on them. And you also have to use a dedicated Controller with a phone-klip or some teleskopic controller like the Saitake 7007x).
For me personally all the available solutions for CM3 (there are only two, that i know of: the Freeplay CM3 and the Retro CM3) are a bit too expensive. At least in my eyes.
If you want a cheap device (below 60-80 € / $) that can play everything up to GBA/SNES (and PS1 with some few exceptions), then i would buy a (new) PocketGo v2 or a RG350.
You can find plenty of information and reviews for those devices on youtube from ETA Prime, Taki Udon, Retro Dodo and others).
But with such a device you have to do without Batocera again.