When I was hired (many years ago) I sucked it up and did the double occupancy thing, but shortly after training ended I got a bill for half because someone made a clerical error and had me down as a single occupant. As I recall they wanted to charge me around $800 for the nearly two months or whatever it was. It was resolved, but I think that's a reasonable price expectation.

Also, consider that once you're done with ground school and move on to the sim, chances are your roommate is going to have a different sim schedule than you and you won't see each other near as much. I remember going a few days at a time without seeing him, but the downside is it was kind of annoying when you're coming in a 2am and he's going out at 4am and you're both inadvertently waking each other up.

I'd probably just pony up for my own room now, but it's a different world when you're on first year pay and walking down to the Taco Bell sounds like a luxury.