Look in your Yellow Pages for a chemical company near you, see if you can buy a 25 or 30 gallon drum of Sodium Hypochlorite, when you buy it this way, you can also get 10% or 12.5%, so therefore you use less and you should be able to buy it cheaper in a 30 gallon drum, if you have a friend that has a pool, buy a 55 gallon drum and you can both use it. With proper storage, it has a good 1 yr shelf life. You can get a drum and an inexpensive hand pump for the bunghole.
i have not actually done this because my pool stays clear and in parameters all year.
The best pool store near my house in Thailand is World Chemical.
I do need to get 2 bags of salt soon and when I go, I will ask about this and see what they have to say and post it here.