I've never priced the liquid, but the powder seems to be pretty cheap. I paid about $15 for 4 pounds of it.
One thing, if you do ever do the sock method with the powdered stuff.... the sock I picked to use was a pretty
thick "winter" type sock. Not crazy thick, but a little heavier than your normal everyday sock. I found after two
days that the majority of the stuff still hadn't dissolved into the water. I had to massage the sock for about five
min to get most of it to come out on day 3. Use a somewhat thinner sock. I hung mine close too, but not
directly in front of the return jet.