Assume it does cost $1bn, then that's 40million rides to break even (obviously a lot of other costs I'm ignoring here). If only 5% of people using OHare (80million) take it, then that's 10 years before it is paid back. Considering this infrastructure should last 50 years minimum, it could well be profit generating or at least revenue neutral.
Musk always runs over budget by a multiple, it’s how he rolls. Maintenance is probably three times or more the initial outlay over a 10 year period. So, it probably won’t be profitable or revenue neutral.
But it shouldn’t be. A brand new transportation mode is going to run at a loss until people figure out how to deploy it at scale. It would be weird for it to be profitable from day one.