Ok, this is probably the worst suggestion ever and I'm guaranteed no's but I was thinking that new MTA players that play MTA for the first time get an opportunity to join a server and if they want to join another server they can simply click no. Think of it this way:
Say that the FFS server pays for this and the money goes to the MTA devs. Also say that I'm new to MTA and I first start it. When I click the Server Browser I would get a notification asking if I would like to try out the FFS server. The notification has a yes and a no button. If I click yes then it brings me to the server. If I say no then I can choose any server I would like. Here are some advantages:
-MTA devs get money
-Servers that are growing get an opportunity to get players
-New players aren't forced to join the server; they can simply click no
-It helps new players choose a server more easily
The money system can be determined by how much the server owner pays. Again, this is just a suggestion and there are many advantages.
Edit: I noticed that if the new player rate isn't that high then everyone will see this then.