When most people talk about this type of juice, what they're actually referencing (probably unknowingly) is a sugar-laden version of cranberry extract mixed with extra sugar. The difference in sugar content between sweetened vs. unsweetened cranberry juice is profound.
The unsweetened version is not sold under many brands. Most brands like Ocean Spray and Langers are almost always a version which involves added sugar. Even the 100% juice varieties have added sweetener in the form of other juices, like apple and pear, to sweeten the beverage.
The brands which truly are 100% unsweetened cranberry juice include R.W. Knuden (a.k.a. Knuden's) "Just Cranberry" which comes in a glass bottle. The ingredients are filtered water and organic cranberry juice, that's it. It's sold in the shelf-stable (non-refrigerated) section of the grocery store. You may be able to find a cheaper generic brand, too. If you shop at Kroger's (or Ralph's in California) then the Simple Truth brand sells a plastic bottle of 100% unsweetened organic cranberry juice.
How much sugar is in them? The natural sugar content is just 7 grams per 8 ounce glass, which puts in perspective just how much sweetener is being added to all the other sweetened varieties (which contain a whopping 30 to 36 grams for the same 8 ounce serving).
All forms, whether with or without added sugar, do have a fair amount of antioxidants in them, as depicted in the ORAC value above. Though pure concord grape and black raspberry juices contain substantially more antioxidants.
USDA Database for the Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 - Prepared by Nutrient Data Laboratory, Beltsville Human Nutrition Research Center (BHNRC), Agricultural Research Service (ARS), U.S. Department of Agriculture (USDA) - May 2010