To compare bleach prices, convert all amounts to a common unit, like ounces (or litres, if you are of that persuasion). Then multiply by the concentration. This will give you how much sodium hypochlorite is in the bottle. Divide the cost by this amount, to give you cost per unit of sodium hypochlorite.

Example:

Say, you are comparing:

3 quarts of 5.25% bleach at $1.33 (found at local Target)
5.43L of 6% bleach at $2.59 (found at local grocery store)
2.5 gallons of 10% bleach at $3.60 (found at a pool store)

(FYI these are prices I found yesterday)

3 quarts = 96 oz. 96 oz. X .0525 = 5.04 oz. 1.33 / 5.04 = .26 cents/oz
5.43L = 181 oz. 181 X .06 = 10.86 oz. 2.59 / 10.86 = .24 cents/oz
2.5 gal = 320 oz. 320 x .10 = 32 oz. 3.60 / 32 = .11 cents/oz

So, the 2.5 gal of 10% is the best deal by far.