You find mechanics do not charge by the hour, they charge by the job. It can be tough to get an estimate before the job, since most do not have enough confidence and skill to be able to determine how long or difficult it will be to fix.
Even folks that buy new are reluctant to take them to dealers for maintenance, due to waiting times and cost for even simple repairs.
As a result, many buy a vehicle and simply drive it until something breaks, then look for a mechanic that will get it back on the road as cheaply as possible.
Having said that, if you come and set up shop in a city like Santiago or Santo Domingo, if you are good, you'll have more work than you know what to do with. You'll also end up with a bunch of repaired vehicles the owners don't have the money to pay.
I once took my Land Rover to Auto Germanica for a repair job. When I went to pick it up, it was in their lot across the street. The lot easily had a hundred vehicles waiting for owners to pay.