Server?

Or just put a password on your server

If you set sv_lan to 1 (which should be enabled by default, but you can check this) then only people in your local area network (such as those connected to the same wi-fi network) can see and connect to your server. Using a password can also keep players out.

I don't think he's asking about hosting a local server to test stuff I think he's actually wanting to host a server.

I think answer is not worth it, game servers are relatively cheap these days

"Relatively cheap" depends on what you want to run on your game server. If you want just a plain server with basic Sourcemod then that's pretty cheap. As soon as you want more stuff like a FastDL, access to put plugins/extensions (executable code), a database, a website, or other things, then the price will start to go up with your wants. Hosts also sometimes overly cram their hardware with many customers' servers so you may not always get good performance (at least for VPS/GSPs, dedicated should be better).

To start with you can try setting up SRCDS on your PC and forward the ports, and then later decide if you want to commit to a game host or not. If you want to do some more research or ask more questions on this subject, check out AlliedModders (developers of Sourcemod and the main go-to place for SRCDS-related questions).