eBay says a Chinese Z80 clone is less than $4 with free shipping. This isn’t even going to be competitive with lower end FPGAs. It’s more of a fun “why not” type of project.
They're ASICs. Likely a direct copy of Zilog's design but I'm sure re-implementations also exist.
I've never received a counterfeit Z80 that outright didn't work, but one thing to be keep in mind is that despite often being branded as CMOS 20Mhz (aka Z84C0020), half the time the chips I've received were lower grade or even worse, NMOS.
