ECC RAM is overkill for a retro gaming server.

No. You don’t need ECC memory for an emulation box.

Emulators are CPU-bound, not memory-error-prone. A flipped bit in a texture or a sound sample might cause a tiny glitch you’d never notice in a retro game. Even in a decade of running emulation servers, nobody has a horror story about non-ECC RAM corrupting their save states.

ECC costs more, can be slower on consumer platforms, and often requires workstation/server motherboards and CPUs that don’t make sense for a gaming server. A regular desktop build with good quality non-ECC RAM will do everything you need.

Don’t over-engineer this. Put the money into a better CPU or more storage.