The 'transformer' story sounds funny ... especially as I know what you want to air condition. Have this checked out by a reliable electrical engineer. Perhaps the North Coasters can supply you with the name of a good ... well, even an electrician will be able to figure it out. But then it must be an electrician that is able to 'figure'. The transformer is a thing that sits outside on the pole, to my knowledge .. and you don't pay for it. If the electrical company put in too small a transformer for your area there, they have to change it out. It is their responsibility. (This sounds awfully like an undocumented 'Gringo' Tax to me!)
For a generator, the size of it must be worked out first. You'll perhaps need something between 10kW and 20kW. (Not sure what the airconditioner will eat up.) There are good places in Santiago to buy a diesel generator, both new and used and Hillbilly can help with names of companies. Again, that good electrician or electrical engineer needs to lend you a helping hand here to work out size, especially with the airconditioner.
You'll perhaps save a lot of money over the long run if you also install a inverter and battery bank at this stage, while you're spending. Most of us have a combination of an inverter and battery bank plus generator.
gary short, with respect, 5kW of Watt? and most of us will not make a recommendation unless we know what the poster wants to power. If you knew about this stuff, you would do an analysis first.