Actually, as someone with "substantial mountain time" (whatever the hell that means) the mountains in Mexico when I was going down there didn't really bother me much. The approaches had a tendency to be a little complex, and the controllers either didn't speak english or didn't know what the hell they were doing, but other than that, it was pretty easy. The runways are all mostly long, the facilities are generally good on the ground, and the approaches, while usually done from the whole procedure, and via some convoluted system of arcs and stepdowns, are by and large straight forward. Mexico isn't that big of a deal. US customs is a pain in the ass, but Mexico is fairly easy other than the sleep deprivation to get down there.
Are you going to go to Priority out of...uhh...I think they're in Ohio?