I'm certain that many Ontario teams would be very willing to help you with the logistics of getting to St. Louis and share our expertise on how to do it best.
However, the bus can wait. As was mentioned above, today (the Tuesday after your event) was the payment deadline for Championship - it is insanely quick after finding out you qualified, especially for a rookie team. If you haven't paid ($5000 USD), your lead mentor needs to contact FRC Team Support first thing tomorrow and see what you can do -
frcteams@usfirst.org or 1(800) 871-8326. They also would have wanted you to ship it in a crate by Thursday.
I would strongly recommend your lead mentor contact FIRST Canada as well, since they can likely help you out - try the director, Mark Breadner (mark.breadner@firstroboticscanada.org) as soon as possible.
As to your question about cost, the price each student will pay is highly dependent on how full your bus is. Expect the bus to be in the ballpark of $6000-$7000 for a charter from Ontario. Sharing with other teams is a definite possibility if you don't have a huge number going. Hotels and food you already heard about.
Feel free to private message me if you have more questions, or post them here. But make sure you get on top of this right away, because we'd hate to see you miss out!