I was doing the same calculations over and over to determine the cheapest cost of bleach for my pool -- so I created a spreadsheet that assists with this and thought I would share it.
If you find a source for bleach (i.e. Walmart or Albertsons) and want to know if it is cheaper that another source -- which happens to be at a different dilution or quantity, you can do that easily with this sheet.
Just enter the concentration (6,10, 12.5%), the quantity (Gallons or Oz), and the price. The sheet will return for you the price you would pay for the same amount of chlorine in various volumes and concentrations.
The sheet is locked (so that you can only enter into the cells that are input and not into formulas) but it is not password protected, so if you want to fiddle with it, you may just unlock it.
Doesn't seem that I can attach it, so I put it up on a webserver here: