I got the following recipe from a Low Carb message board. It's simple and relatively inexpensive. Do a search for "homemade low carb milk", there are probably more than just this one. Another alternative is Blue Diamond unsweetened almond milk It's really good, but you may have to order online. It does have a slight almond flavor, but it is not that big of a deal.
Homemade Low Carb Milk
1-2 Tbs. of heavy cream (depending on how creamy you want it)
1 1/3 Tbs. of instant dry milk
1 cup of cold water
sprinkle of salt
tiny sprinkle of splenda (if you want)
Just put the ingredients in and shake it up. Refrigerate.
Calories 65 if 1 Tbs. of cream is used, 110 if 2 Tbs. of cream is used
5 grams of fat / 10 grams of fat
3 carbs / 3 carbs
2 grams of protein / 2 grams of protein
Of course, you can double/triple, etc. the recipe. But it's pretty cheap to make.