Apparently, I'm an oddity. My local pool store refills 2.5 gallon (320 oz) containers for $5, and it's 10% chlorine, which, if my math is correct, gives me a cost per ounce of about 16 cents. (I think the initial cost to buy the container was $8, but that was 2 years ago). They also have a punch card - after 10 refills, your 11th is free.