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: https://a.co/d/ibaXWkT
vs.
Raw board for $80 to kits from $155 to $165:
https://www.canakit.com/raspberry-pi-5-8gb.html
Then install RetroPi:
And supply ROMS to it.