A lot of it depends on what consoles you want to emulate. I’m no expert, but from what I’ve seen just casually looking through retro gaming forums, is that anything up to N64/PS3 is doable with relatively cheap hardware. But if you want to emulate N64 or PS3 and above properly, you’re going to need to step up in specs.
Thinking of getting a retro gaming machine.
Maybe I‘ll mod my ps3 to make it emulate games. I heard that works pretty good....