On any used MH there is no hard fast rule. You might find a high end coach with only 12k miles....problem it was a snowbird coach that went from warm to warm and was lived in full time. You might find a 80k mile coach with no signs of wear(nascar fan went to the races came home) (you can also use golf, football etc)The mechs of the modern DP drive train are good for million miles with proper maint. which is not that bad. All other systems fail reguardless of brand.
These things break so just be ready.
This is not about cost, you will loose, this not about reliabilty you will spend a night or two at the repair shop, this is about the trip and the road and what you will find.
Bring 1/2 as many clothes and twice as much money:)
Jim