Diesel pushers usually have turbos whereas gas motors do not. Diesel pushers usually have air suspension and gas motorhomes usually do not. I replaced a turbo intercooler last year, had my radiator rodded, and adjusted the valves and it was 8 grand.
In my opinion 50,000 a year is plenty. But I think it is unrealistic to think maintenance and repair costs are similar on diesel or gas motorhomes. That is not my experience. On a new rig with a warranty then the cost will be closer.
But 50 is enough for either. That is unless you camp at casinos and have the gambling bug. Then 500,00 is not enough. LOL.