Mexican Coke can operate as a barometer for how expensive the restaurant you're visiting is.

Mexican Coke generally costs around 69 cents and probably even cheaper if you purchase in bulk.

If MC costs more then 3 x 69 cents  ($2.07), then it can be safe to assume that, not only is the MC overpriced, but the restaurant you're at also is.

Anything more than 5x 69 ($3.45) cents, and the restaurant you're at probably has a lease that is oppressive and a menu that is trying to make up for that.