I’m sad nobody else responded to this, but i’ll share my favorite:

https://www.hardkernel.com/shop/odroid-go-advance-black-edition-clear-white/

They had a black friday sale on these last year for $30, there’s a newer version with a larger screen but same cpu. They ship a retroarch install tailored for the hardware, it’s great.

Alternately, stick your phone in like a Razer Kishi and use Lemuroid: https://github.com/Swordfish90/Lemuroid