$29.99/core dedicated hosting: a whole
physical core of a Ryzen 9 7950X, no oversell, with 8 GB RAM bundled per core. Tell us your group size for a
recommendation and pick your cores; RAM is auto-sized and included, nothing to tune. Run it always-on, or
ad hoc, metered by the hour and billed only while the world is actually up.
Without one the server plays perfectly well and anyone you give the address to can join. What you lose is the public server browser: Steam applies a severe ranking penalty to anonymous servers, and a player's Favorites entry will not follow the server if its address ever changes. Worth doing for a public community server, pointless for six friends joining by address. It is free, it takes about a minute, and it has to be yours: the game ties it to your own account, so we are not allowed to issue one for you. You will also need a separate one for each server you run.
Sign in at steamcommunity.com/dev/managegameservers with the Steam account that owns Garry's Mod.
Create a token with App ID 4000, and give it a memo naming this server. 4000 is the game itself; 4020 is the dedicated server tool, and a token made against 4020 is rejected by the server.
Paste it into Steam Account Token on this server's Settings tab, then Restart.
One token per server, and Steam expires a token that goes unused for a long time.
Resetting your Steam password regenerates every token on the account, which quietly drops an already-listed server out of the browser.
There is nothing to wait for in the meantime: the server is joinable now. Give people the address from the Connect tab and they can play while you decide whether public listing matters to you.
Auto-sized to your game: 8 GB bundled per core, no RAM to pick and nothing extra to pay.