It will support itself by charging for optional expansions, though the first add-on will be released for free. Steam is currently running a sale.
Until now you had to pay monthly subscriptions if you wanted access to certain features like the Agency vs. Agency metagame but it'll all be available now. Hi-Rez hope to profit from the expansions they have planned, and most likely from microtransactions.
Currently Steam has a summer sale on withhit with a 33% discount - which brings the game down to £16.74. Check out the game's launch trailer.