Ditto on Interstate.
The price the dealer is suggested includes enough profit to install the battery. If call your local Interstate dealers, and tell them your shopping for the best price, cash and carry. At least one will probably take the bait, and offer you a better price than the suggested retail.
There are 2 places I can get them in my area, and save about 15-20% that way.
A second tip is always put in the largest battery your vehicle can hold. Most vehicles come with a battery, from the factory, that is smaller than the battery box is capable of holding. A larger battery will be capable of withstanding accidentally parking the car with the lights on better, and will still be able to start you car as it ages and loses some of its capacity.