I just got back from a week in the 'World, and while I didn't encounter any disgusting bathrooms, I would say virtually every time I was in one, it was at least somewhat less than clean - a few paper towels on the floor, perhaps - puddles of something here or there. I would say they were all roughly on par with what you'd expect running into a random McDonald's anywhere in the US.
So I agree with other posters who have suggested that an above-average cleanliness should be expected for the price of a WDW experience.
I don't know the exact numbers, but I'll ballpark about 20 restroom areas in the Magic Kingdom. If, during peak times of the year, you hired staff to maintain at least one person for each bathroom area, 15 hours a day, at $20/hr cost to Disney (all numbers rough guesses), that's still only $6,000 a day. If you consider there are probably an extra 10,000 people visiting during these times, that's a cost to Disney of less than a dollar per person to have the bathrooms well maintained.