You can implement a system that allows players to donate for the community server, simply to keep it alive.
Another thought I have is that, but it might sound stupid, to make a RuneScape 07 based server available to anyone, more like a "Wilderness"-server.
It could serve as a advertisement for OSBot(Having OSBot in the name of the server, or a link to this forum anywhere on the site), so you can ask Maldesto to get you a budget to start off with.