@DarkScribe, “expensive Mexican Restaurants” may be something that only occurs in the States near Mexico. (You can also get really good cheap Mexican food in the Southwest, so I think it’s more demand than anything else.)
I think part of the issue with the more expensive places (not chain restaurants) is that the food is less regimented than in fast-food type joints: sort of like how, at a Starbucks in California and a Starbucks in New York, a Caramel Macchiato will taste (basically) the same. There’s a “formula” or “recipe”, if you will, that the chain stores aren’t allowed to deviate from.
And to me, expensive is upwards of $50 for 2–3 people. (Is that expensive? I have no idea, as I rarely, if ever, eat out on my own. Usually it’s family taking me out, for my birthday or something.)