In a medium bowl, mix the cranberries with 1 tablespoon of lime juice. Drain off the lime juice and toss the cranberries with 2 tablespoons of sugar. Spread them out on a baking sheet to dry.
Mix the remaining sugar with salt on a shallow plate. Use the lime wedge to wet the rims of each glass, then dip them into the sugar-salt mixture.
In a large blender, combine the cranberry juice, tequila, triple sec, remaining 1/2 cup of lime juice, and ice. You may need to work in batches if your blender isn't large enough. Blend until smooth.
Pour the mixture into the prepared glasses and garnish each with a sprig of mint and a few sugared cranberries. Enjoy your delicious cranberry margaritas!