It isn't the liqour that costs so much for margaritas, it's the mix. Calculate the cost of the liquor in a margarita, and I bet the mix cost a similar amount. It is easiest to use sour mix with a splash of Sprite or Soda Water and a splash of Roses lime juice, and IMO, it makes for a much better Margarita. You can ditch the Cointreau if you are using Grand Marnier. There is no need for two orange liquors in a Margarita. ;-)