I find it hard to believe that a City would organize day laborers and require that they earn $20/hr. Vista has set forth some regulations that require anyone who picks up a day laborer have a license to do so (you can get the license for free at the City). A contract must also be signed between the homeowner and the laborer that describes the work to be done, how long it will last and the amount of pay. I don’t think there were any requirements on the pay, just whatever was agreed upon.
In Powayseller’s case, if you hired a company to clean your home and they sent out someone to do it, it’s totally reasonable that it would cost $18/hr. That would be the total cost (worker’s wage, worker’s comp, benefits, company overhead, etc.) The worker would probably take home $8-10/hr