Don't know what chassis you have but on my Workhorse chassis, my rotors are still good at 90,000 miles altho I changed pads at about 50,000.
On the side of the rotor is the MINIMUM size mark to which they can be turned and still used. A lot of mechanics would rather replace rather than resurface old rotors, especially if they do not have the equipment.
The choice is up to you but most places will charge $100+ for each new rotor and the cost to turn each rotor could be as low as $25 each and some shops have the equipment to turn the rotors while still on the vehicle.
Brakes are one of those things that a lot of shops really love to use as a cost upgrade to the customer. Once it is apart, they may say you need new calipers, new brake lines, new bearings and seals, etc. The next thing you know, that low estimate for your brake work has skyrocketed to $2000-$3000.
I'm not saying that those things may not be required on your coach, but make sure that you are not paying to replace parts that are perfectly good.
Also make sure that they FLUSH the old brake fluid and do not just bleed the brakes, leaving most of the old fluid intact.