I'm wondering how many mowings you'd need to make to pay off the difference in a diesel versus gasser mower. Anyone care to take a stab at it? Mileage is better, but diesel isn't exactly free, either. I mow 3-4 acres every 3 - 5 days, and I don't think I could manage to rack up enough in fuel savings to offset the higher price of the diesel, I'm guessing only a commercial outfit is going to be able to make those numbers work.
As to maintenance, I've owned my mower almost 20 years, and have not had a single expense related to the engine, other than yearly oil and filter.