You SHOULD go to Mexico, place like Toluca, Puebla, Tlaxcala, Zapotecas are amazing running spots, and those places are SAFE, Mexico has a way better running scene and running culture than the andean countries, so you WILL find a training group easily.
There is a LOT OF road races if you want to test your fitness, road race are more popular than track because most mexican runners focus on the 10k HM and marathon, the depth of mexican long distance running isn't as good as it used to be but you will eventually find training partner of your level. Mexicans are REALLY NICE and open to foreing people some of them speak english it's way easier to find an english speaker in Mexico than Bolivia Peru... (not sure about some places like Bolivia or Peru where most of the population is rural) they will welcome you, and treat you like as if you were a long time friend.
Altitude in Mexico might not be as high as La Paz, but you can train in pretty high places, Toluca is 2640m most of the top mexicans train there and even some kenyans (running marathon for most of them between 2.35 and 2.10). Zapotecas is 2400m, Puebla 2100, Tlaxcala 2600 in this state you can find a pretty good training center with a track located at 3000m of the flanks of a volcano called La Malinche not sure about the price but it shouldn't be so expensive).
To conclude, Mexico is a pretty damn good country to live, I would not spend my entire life there, but I spend amazing time there, country is beautiful, people are nice, some womens are so fucking beautiful in some parts of the republic, the country has pretty good infrastructure facilities (which Bolivia hasn't) you can travel in the whole country pretty easily by bus mostly or plane, you can find various running park in most of the big city (Guadalajara, Puebla, Mexico city, Monterrey)or train on the trail if you have a car it's pretty easy to drive one hour and reach a mountain from Mexico city or Puebla . There is some pretty nice colonial town, and a lot of history.
Source: I lived in Mexico (Puebla during almost a year).