I'm not sure a homeless guy would accept $5 a day to sanitize the bathroom completely after every use. I don't think he would do near as good a job as the machine would if he did. I also don't think people would have the level of trust that he did.
You have to understand maintaining a clean restroom facility open 24 hours a day/365 days a year to anyone and everyone is very difficult. There is also overhead in the supplies used. I don't know if supplies are included in the cost, but the proposed bathrooms efficiency is probably much greater than that of a human attempting the job by hand.
When you think of two bathrooms, it doesn't sound like a lot for $500,000 but if you start to factor in the length of time, the unenviable task of cleaning it after every use, and the glaring need it starts making more sense.
This is not a quick fix, or a kids band aid for the problem. This is the real deal and a solution to the problem. I'm not sure how much impact 2 bathrooms can make on an entire city, but it's a lot better than 0 bathrooms.