I'm on my 2nd Beaver the first a 2000 PT and now the 2002 Marquis...both great and would do either again in a heartbeat.
Like boats, I automatically allow 10% of the cost for immediate maintenance and upgrades and so far that has been a smart move since there are always thing you want to do to make it your own.
Both of mine have had the Cat C-12 and Allison 4000. Excellent on power and reliability plus a true compression brake.
I believe the comparable Monaco models would be the Dynasty and Signature respectively.
Once you get the initial kinks worked out, figure around 1K per year for maintenance not counting batteries, tires, and etc. Than kick back and enjoy the ride and comfort.