you're pretty much stuck buying new steer tires for the front of your bus. It's difficult to come across GOOD used steer tires. They're pretty expensive...prob at least $200-300 per tire. That being said, I have to admit, that i have a used steer tire on the front of my bus. it's the best tire on the bus though!
The good news is that you can find rear tires for cheap. Simply go to the big truck tire store and tell them you are looking for some used rear tires. I bought one for my bus in michigan for $80, and another one when i was out in LA and that one also cost me $80. Be careful.....In cali, 80 dollars covered the new (used) tire, mounting it on the rim, and removal,installation on the bus. The tire i bought in michgian really cost me $120. 80 for the tire, 20 to mount it on the rim, and 20 more to remove/install it on the bus. UGGGG!
I would suggest watching the tire guy remove and re-install the wheel on yoru bus the first time if you're not familiar with the process. If you ask, he'll prob even give you a short tutorial. It's not that difficult, but if you're not careful you can easily remove your kneecap in the process.
I've changed skoolie tires myself, but most times its just easier to have the pro's do it. Especially if you have good sam emergency roadside assistance. IF you have a rear dual tire go flat, you can usually drive a significant distance to get to the big truck tire store.
Quis custodiet ipsos custodes (who will watch the watchmen?)