Of course it depends on the size dog food bag but from what I seen it is between 11.98 for the small bag to the 30 lb bag at $54.00.
Bathing twice a week is too often. You should only bathe them when they are dirty. It can be a month or more depending on where they play and what they get into.
If you get a good brand of shampoo, without detergent, you will not be so likely to wash away the oils. You can put a little shampoo in a glass or bottle and add water to make it last longer. It does not hurt anything to do this. I always dilute the shampoo and conditioner.
I use Isle Of Dogs shampoo. It is expensive, it is not in any stores but you can have it shipped to you. This will last you for years if you buy the big bottle, $25.00. A good shampoo will pay for itself by making your dog more comfortable.
There are good shampoos out there in the stores but stay away from the cheaper brands. You can also use Treseeme human shampoo. I know a few show people that use that. And that would be a cheaper solution. Again dilute it.
Your dog is going to have to have oil added to its food to cut down on the flaking and itching too. I think WalMart has Lambert Kay oil supplement and that is a wonderful brand. If not Petco and Petsmart will have something to add to the food for oil. If you get the Natural Balance dog food you won't have to buy the oil.
If you don't mind ordering from the internet go to
PetEdge.com Wholesale prices on exclusive dog grooming and pet supplies They are the cheapest place that I have found and that is where I get 90% of my stuff.