It's my understanding that mariachi music originated in Guadalajara, although I'm no expert. But we have lots and lots of it here in Houston: at Mexican restaurants (of which there are literally hundreds) and on TV, and at pretty much any local festival. And although all the bands do some instrumentals, I've never heard one which didn't rely mostly on vocals, whether good or bad. An instrument not mentioned thus far in this discussion and which is almost universally used here and in Mexico is a nylon string harp. Some of the traditional songs, like "La Barca de Oro" or "Malaguena Salerosa" are just beautiful and quality of their performance is a test of the band's singing skill. Oh, and if you ask a band to play a particular number they expect payment. The going rate here is about $5 per song.