I get the 5 gallon jug at the pool store (yes, gasp!). 12.25% which probably comes down to 10 or 11% in reality since there's some degradation of the concentration with time and heat. I paid a $5 deposit for the carboy initially and trade it in for a full one for $14. That comes out to $2.80 per gallon or $0.0218/oz.
I did some calculations a while ago using cost/oz for the various concentrations of liquid bleach and how much I need to add to my pool to raise it by 1 ppm, and I found that using pool store chlorine was the least costly, even when I assumed a 10% concentration. I have a pool store nearby, easier to get to than the x-marts, so for me, this is the better deal. YMMV.
AnnaK