Most folks make their own with a Raspberry Pi and a “RetroPi” installation. You source the ROMS yourself.

There are pre-loaded kits, but they are many times more expensive than DIY.

$400 on Amazon: a.co/d/ibaXWkT

vs.

Raw board for $80 to kits from $155 to $165:

www.canakit.com/raspberry-pi-5-8gb.html

Then install RetroPi:

retropie.org.uk

And supply ROMS to it.