It really is very simple math if some realism is applied, and ownership planned on long-term and not trading every few years for shiny-new-thing-i-tis.
I bought my small Class C new for $55k in cash back in 2011; it had a sticker of $78k. I expect to keep it for 12 years and somewhere between 90k and 100k miles. I'm halfway there now at 6+ years and 47k. Since I maintain it well, everything should work at that point, and I expect to be able to sell it for about $15k then. Basic math: $40k/12 = $3300 annual depreciation costs.