I don't buy juice very often, though I really do love the stuff. Frankly, it just isn't very cost friendly. And it isn't really very good for you either. Fruit juice has all the "bad" parts of the piece of fruits, with out much of the good stuff. You get the sugar but none of the fiber. You do get the vitamins and flavor though.
When I do buy juice, I have found that the least expensive way to do so it to get it in frozen concentrate. It usually comes out to about $1.00 less per container. They are also super easy to keep in the freezer and pull one out whenever we are in the mood for a glass of juice with breakfast.
Also, one way you can save your self a little more money is to dilute it just a little bit more than is called for. Most frozen juice concentrates call to be mixed with three containers of water. Instead of the three, I usually do four and sometimes even 5, depending on the strength of the juice being used. I find the flavor to be strong enough and it makes it go that much further.
Also, make sure you are buying 100% juice!! We seriously don't need any more high fructose corn syrup in our diets and that is pretty much all you are getting with juices that aren't 100%. Would you buy an apple that wasn't 100% fruit?