Since you asked, we purchased our bus in September, 2007 and have spent $15,379.64 so far.
And we have several maintenance issues yet to be addressed before we hit the road this season.
And we have not yet spent any money on tires or batteries as I had expected. Although that day is soon approaching and will add about $9,000 to the total bill.
However, that being said, a substantial percentage of this was spent on repairs/upgrades that will never need to be repeated in our lifetime of owning this bus.
I also don't personally consider the depreciation as a factor. To us, it's simply part of the cost of enjoying this lifestyle. Since we live in the bus full time, we figure that we aren't maintaining another "house" somewhere.... so no need to worry about replacing the roof or furnace or plumbing or whatever.
Think of the money we've saved in snow shovels, lawn mowers and leaf rakes!
And, the experiences we've had, the places we've seen and the friends we've made are priceless.
Good luck in your shopping..... go for it!