Please dont buy pre-made protein shakes, not only are they a waste of money but most of them are horribly unhealthy – just read the label that has a list of ingredients as long as a roll of toilet paper!
You can make your own protein shake for 60 cents with just a banana, scoop of protein powder, and 8oz of milk, soy milk or juice. If you have the money and are health conscious, you can use organic stuff and that will up the cost but it will still be a lot cheaper than anything pre-made.
A few words about flavor mixing, you gotta be careful about mixing flavors. If you have chocolate protein powder, then its best to stick to neutral tasting liquids like milk. If you have the vanilla protein powder, you can use juices as well.
And remember, there is nothing magical about a protein shake – its just a meal replacement! Some people fall for the ads and start believing that shakes have some magical muscle building properties, not true. Massive, one time doses of protein dont do any good and they just turn into very expensive urine. You need your protein spread out in little doses every 2-3 hours. If you want to know how many calories and how much protein should be in your shake, use my meal calculator.
There are some that are concerned about mixing acidic juices (like orange juice) with protein powder for fear it will curdle and destroy the protein powder. In my experience, it causes no problem but avoid using juices if you are concerned.