• RESORT-STYLE FROZEN DRINKS: Margarita Girl's Single Mini Slushy Machine turns your favorite beverage into a resort-style frozen slushy. Delight your guests with a variety of alcoholic and non-alcoholic frozen drinks. This high-capacity residential-grade model does not use ice or an external water line and makes up to 25 cups of frozen margaritas, daiquiris, piña coladas, and more to keep the party going!
• EASY TO OPERATE AND CLEAN: Simply pour your favorite drink mix, wine cooler, soda pop, or clear juice into the bowl and turn the machine on. Your frozen slush drinks will be ready to serve in just 75-90 minutes. Avoid diet/low-calorie/skinny beverages which typically do not slush well. Dispense any remaining mix into a pitcher and store in the fridge for later use. 
• TECHNICAL SPECIFICATIONS: This versatile frozen drink machine features a 1.6-gallon bowl, an intuitive control panel, and a 1/5-HP air-cooled compressor. It plugs in to a standard 115V household power outlet. It weighs 40 lbs. and measures approximately 20” high x 10” wide x 12” deep. 

This is for the machine ONLY. Mix and Alcohol NOT included.The Machine holds 3.2 gallon

Most of the Ready to Drink Margaritas from the liquor stores are 1.75L.
If you went this route, it would hold about 3 of theses at one time. (1.75L = .46 gallon)

Alternatively, you can use a 2 parts mix (2 - 1.75 bottles) mix to 1 part tequila (1.75 bottle) ratio. 
This would give you a total of 1.38 gallons. Adjust the amount based on your preference for a stronger or milder tequila flavor.