Here is my 2¢, We live in our bus fulltime, so our milage is minimal. We got a bus in good condition and believe it was well maintained. Being stationary fulltimers (military) we maintain based on time rather than miles. I just had my first annual done, and it was just under $1k. Also got oil analyzed at purchase and at recent service, very good results and I get that warm fuzzy. (even watched them pour it straight from the quart jug to the sample bottle) For everything in our first year of ownership, we've spent just over $3k. A LOT of that was non maintenance related stuff and fuel for montly runs, so your milage may vary.
Geoff