This year I built a budget mini-pc dedicated to retro gaming, just for emulation using LaunchBox/BigBox and RetroArch.
It has not much horse-power, about PS4 performance level at an estimated 1.9Tflops, but it's in a very tiny build!
It works great (with a very little tweaking) out of the box and it is connected to a 65" 4K TV.
MiniPC specs:
APU: AMD Ryzen 5 3400G (4 cores / 8 threads @3.7Ghz) with iGPU RX Vega11 (11 cores @1400Mhz) - €135
RAM: 8Gbyte DDR4 @2933Mhz - €70
Disk: 1x SSD (1Tbyte) - €90
Mini Barebone: AsRock Deskmini A300 (MB Asrock a300, integrated Realtek HD soundboard, stock cooler) (No overclocking possible) - €140
Total cost: about €435 (less then $400)
It runs games from Atari 2600 up to the Arcades, PSX, Saturn, N64, Dreamcast and PSP at fullspeed.
At native resolution works well also for PS2, Gamecube and Wii games emulation.