It is much cheaper. If you moved to Vancouver you would spend a million for a dump. In Mexico you can live like a prince on the cheap. Just steer clear of the drug gangs.
It's not as cheap as it was just ten years ago. Still it's better than any of the high cost of living big cities in the states. Plus the weather is a huge bonus as long as you can avoid being there during the rainy season. November thru April is ideal.