This seems like a possible choice for 30A only.
Using 2 for 50A would be about $600. And I'm not sure that 2 of these will work on 50A because it's 120/240 with a common neutral. But maybe I don't understand how it could be used.
It is all in the wiring. If you do not understand it you need an electrician to wire it.
You will rarely if ever see 50amp in Mexico. To get two legs going to your two 50amp RV legs you would need to wire the unit internally so that you plug into a 15, 20, 30 amp pedestal in Mexico and then have it come out the other side to a 50amp socket - which would mean the feed from the pedestal is then split internally in the wiring. Trust me - it can be done.
But if you want true 50amp for use in the US you WOULD need two units and you would need the larger units if you really need the two 50amp feeds - for a total of 100amps. But we only use ours in Mexico and on some rare occasions in the US when we have inadequate RV park wiring - which is usually not on 50amp circuits - older campgrounds with bad wiring only.
It can be complicated - but it works. I wired my own but I have been doing wiring for most of my life and was trained as an electronics technician by the US Navy - so I probably have a better idea of how to do it. An electrician should be able to wire so you have your basic 15, 20, 30amp feed in Mexico come out of the regulator so you just plug in your 50amp RV plug to the regulator outlet. We have been using ours for several years so I know it works. You will NOT get 50amp out if you feed 15, 20, 30 amp in - which is what we usually get in Mexico.