> IP bans only go so far with VPNs costing $2 these days.

https://redman.xyz/doku.php/schachtmeister2 was made specifically against people using VPNs.

It was made for Tremulous (ioquake3 fork) where people kept evading IP bans, but it can be used for any other games.

It is not my project, but I know the author, and I could personally fork it and make it suitable for specific (or any) games if there is demand for it.

You may also use heuristics, too, in schachtmeister2:

  whois   -10     "Hosting"
  whois   -10     "hosting"
  whois   -7      "Server"
  whois   -4      "server"
  whois   -10     "VPS"
  whois   -13     "VPN"
  whois   -3      "Private Network"
  whois   +7      "residential"
  whois   +7      "Residential"
  whois   -20     "Dedicated Server"

Edit: I noticed that the git repository returns 502, contacted the maintainer.