We have had one major breakdown...its outlined here: RV Breakdown - Not Enough Muscles in those Arms
Our other major maintenance cost was replacing all of the tires, which we knew would have to be done when we bought our rig.
We drive ours a lot! We travel, criss crossing the county putting on tens of thousands of miles each year and the only real major expense has been fuel. Sure we've replaced some light bulbs, switches, one side of the windshield (cracked) and normal PM (oil & filter changes). But it is still cheaper than the costs associated with living in our B&S.
Like any machinery it needs to be used...and you need to monitor everything and address those little issues before they become big ones. I
I've seen so many who don't know jack about their rigs except where to put in the fuel and where the beer is kept. Their ignorance of their rig is only heightened by their stubborn attitude of not wanting to listen or learn so they can help themselves to prevent costly failures.