The $15-$20 range was my own initial guess of the ballpark, but it might end up being slightly more.
The captain (or anyone else) can indeed betray the crew. The consequences of that depend on the server you're playing on: some servers are more strict and may kick you for actively trying to sabotage the mission, others may have the traitor feature enabled and only allow sabotage if it's required by your secret traitor objective, and on some servers anything goes.