The prices sounds about right.
Steven, there is a simple way for a dog to lose weight (unless there is underlying medical condition of course)...FEED LESS!
There is no excuse for a fat dog. It is not good for them, and you are doing them an injustice in my opinion. Being a bit too thin is healthier than being a bit too fat, especially with big dogs that have a lot of pressure on their bones and joints.
When I adopted Roxy she was 10 lbs overweight. She was free fed before, and overindulged. I had her down to her current healthy weight in about 6 weeks. Just cut down your dog's food by a little bit, and allow her to lose the weight slowly. Some extra exercise doesn't hurt either!