I have never read a cost justification on any RV that makes sense to me, however you crank the numbers. Cost justification is an investment concept, not a recreational/entertainment concept.
If you buy used and have DIY skills that helps a lot.
If what you buy is unfit for the purpose, it probably is because you focused too much on reading the pros and cons of each class AND asking for advice from others. It is best to get out there and gain some personal experience...that costs whether you get it by buying or renting.