Here are the links, both to Sams and Amazon:

Sodium dichloroisocyanurate (Dichlor) -- 55% available chlorine
PoolBrand dichlor bagged shock 24lbs @ Sams Club => ~$2.50/lb (Jul 2013 in Chattanooga)

Kem-Tek dichlor 2 lbs @ Amazon => ~$6.50/lb (Jul 2013)
Kem-Tek dichlor 5 lbs @ Amazon => ~$4.50/lb (Jul 2013)
Kem-Tek dichlor 12 lbs @ Amazon => ~$4.00/lb (Jul 2013)
Kem-Tek dichlor 22 lbs @ Amazon => ~$3.60/lb (Jul 2013)

Nava dichlor Chlorinating Shock 1lb @ Amazon => ~$4.99/lb (Jul 2013)