Best I can tell, in this part of Mexico, skilled marine labor makes around $1300-$1500 pesos/day, around $70-$80 USD per day. Includes tools, but not consumables or parts. Specialized work like specific mechanics are double that. Apprentice labor is half that. The half-assed guys I initially started with (NizaMarine.net) tried to pay $350-$500 pesos/day ($15-$30 usd) which explains the poor results I received. In other parts of Mexico, going day-rates are half what they are this close to the border. Baja Naval, the nicer yard in Ensenada, advertises general labor at $33/hr.
While I have no direct knowledge, work done in a marina would incur fees paid by the worker to the marina manager. I don't know how much this might be, but it's not zero.
In Mexico, everyone wets their beak a bit, which is fine. Nothing untoward, just how things work here.
Peter.