I tried this and enjoyed it a lot. I used a silver Tequila called Scorpion and Cointreau. I couldn't find any triple sec in the shop I was in at the time. The Cointreau wasn't too expensive, about $15 US the Tequila was less than twenty. Actually the most expensive componant was the Lime. Nearly a buck fifty each. And they were little. I got about 40 ml out of one lime.
2 oz. tequilla*
1 oz. triple sec or Cointreau**
1 oz. fresh lime juice
Margarita glass rimmed with lime and dipped in coarse salt
Shake ingredients hard 30-45 seconds with 6-8 ice cubes, strain into glass, add melted and broken remains of ice cubes. (This is a kind of cross between a frozen margarita on one served "up.")
Garnish with lime slice.
* We use Sauza tequilla for ordinary margaritas, Sauza Hornitos for special ones
**Again, good triple sec for ordinary ones (I use Stock, which seems somewhat better than domestic, sticky sweet ones), and Cointreau for special occasions.