I bet if you asked most owners after they've been through this process if it was worth it most would say yes.
From time to time I wouldn't say frequent or on a regular basis but there are some amazing really really well kept sharp mid 90s Prevost conversions with 60 series in them that people pick up for peanuts. It would require to be quick with an advertisement or a personal referral. The XL and the XLV with the 60 series Detroit (94 TO 2000) r bus chassis that will take their rightful place in history and deservedly so.
If you can find a bus from somebody who's had a few of them that usually turns out well.
Another mitigating Factor 2 your maintenance costs after purchase is directly related to your skill level mechanically and technically if you know how to use a meter and you're good with tools and you can do your own work it's going to be a lot less then somebody who has to rely on a service center to do everything. If you fall in the category of being handy those estimates I suggested could be dramatically reduced.