what is the cheapest bus company to use to make the trips to diffirent regionals? put in sme links please.
If the competition is in your state and you can talk your school district into it, take school buses.
Even though they’re picking up the tab for the driver, gas, and other expenses, the school bus would still be much cheaper than the chartered bus.
And carpooling works well too. 
The only answer I can give you is that you will have to call around.
Depending where you are you may have some local charter bus companys (there are two that I know of where I am). Prices will vary depending on when the bus is needed, how long (duration of time) it will be needed, number of people going, and which bus company you chose.
Remember that with most (if not all) bus companies you will also have to figure in driver expenses including room if staying overnight and meals.
If you are with a school, you first need to get the approved contractor list from them. Then you need to call around. Prices will fluctuate greatly, so it is worth spending the time calling. Get some help from parents. Make a matrix so you are asking the same questions for each. Overnights will usually also include paying for driver room. Long distances may include 2 drivers. Ask for a reference. Some will have a set amount of hours and then charge a large amount for overtime.
Is there another team within an hour of you that might be doing the same trip that you could share a bus?
Good luck.
Have one of your non-engineering adult mentors join NEMO. They have to sign up on CD first. Then contact me. We talk about this stuff all the time.