This isn't really Mexican food but it has Mexican ingredients... Also off the top of my head as the cookbook disappeared in my divorce...

1 ready-made pizza crust
1 can refried beans (I use the vegetarian kind since I'm a vegetarian but I'm sure the traditional ones work too.)
1 jar salsa or container fresh salsa, preferably a bit on the chunky side (or use your own salsa recipe if you're really ambitious.)
Shredded cheese

Spread beans over pizza crust and spread salsa over beans. Sprinkle cheese over that and put it a 350 degree oven until bubbly. It actually tastes surprisingly good even without the cheese, though you want to be careful not to overcook it. And if you're not a vegetarian you could presumably brown some meat and put that under the cheese.

Again, not exactly "Mexican food" but pretty good and not too expensive if you can get a pizza crust that doesn't cost too much.