"The Mendoza line for picking up money out of a urinal trough is 40 cents...hehe"
I don't think that was very scientific. The guy might have been willing to go for a nickel had he been there earlier. :)
You assume it was the amount, but maybe it was just the guy.
It could have also been the amount of beer consumed by the time it reached 40 cents.... so it could be the level of intoxication it took for someone to stick his hand in there.
I would encourage you... next time, closely monitor the restroom, then ask the eventual chump to answer your survey.
This is, after all, for science! :)