I'm with BK on this (especially the cheap part
Sitting for 3 years. . . . . That'd make me very nervous as to the condition of seals & air lines.
Do your homework & verify the bus airs up & rolls before you schedule a tow, you don't want to pay the tow driver his rate to do the things you can!
I used a generator & a portable air compressor to air up one that had been sitting for 10+ years.
You'll be happiest with a Landoll trailer, you won't have to worry about the tires, or air lines, or airbags, or etc during the trip.
(A inside dual tire failure can take out the airbags before you know it lost air.)
Those tow truck drivers MOVE! They don't waste any time going down the road, so if on the hook, your tires better be up to the task!
Landoll tows around here (south east) run from $75 to $125 per hour the truck is away from the shop. So the quote you got is right in line.
The hook tow trucks are ~25% more & some won't even hook up to an old bus. . . .
Did you explain how old the bus is, where it is, how long its been sitting? These things may have an impact on getting it towed. You don't want to pay them just to come out & say "we don't do that".
About the debate over using roadside assistance to pay for towing something you bought knowing it needed towing - I'm surprised there is anything to discuss. We should all know the difference between right & wrong . . . . & where deception belongs.
Oh yeah, about recommending using a vehicle rated for 12,500# gcvw to move a 30,000# 'trailer' 50 miles . . . . Not on MY life! Moving that off the road or short distances is one thing, but when you get to double digit miles, the odds of burning up something move too close to a sure thing.