Mr.Mark scored another "Shot and a Goal"!
$150,000.00 will get you a 1995 to 1999 Prevost 40' or 45' bus conversion with a Detroit Series 60 diesel. The chassis is rated for 3,000,000,000 miles and the engine and drivetrain for 1,000,000,000 miles. In between those numbers you will have maintenance to perform and things to fix and replace. But you will also have something that will hold its value as its depreciation is all but over!
You have concerns with any 17 to 20 year old motor vertical and as Mr.Mark said, unless the Prevost has impeccable records with new tires, batteries etc, plan on $30,000.00 right up front to "zero it out" to bring it up to LIKE NEW standards. In that process if there are any other things the coach needs, it will be found in the zeroing process. Just remember it will be your responsibility to make sure the interior is right. It all needs to work!