For the 2014 season, in order to get to the Northern Lights regional, 2220 used two district minibuses, a coach bus, and a mentor's truck pulling a trailer. I think somewhere around 70-80 students and mentors were in team-provided transportation, and the rest got up to Duluth via self-transport (it's around 2-3 hours from our area). The first time we went up, it was a school bus, some minivans, and a pickup truck. Whatever you end up doing this year, take notes and refine it for the next year. Robots, ice cream, and team transportation are all iterative processes
I would highly recommend starting to try to secure funding now if you plan to use a coach bus to get to a competition. They're expensive, but there isn't a much easier way to transport a lot of kids somewhere. If you don't have enough people to fill a bus, talk to other teams in your area and try to arrange to split the costs.
Also make sure that if you aren't taking the whole team up Wednesday, you know how the people that are going up are getting there. Some districts have rather strict rules regarding student transportation-- don't run afoul of them!