I found that in Lowes today, too. $7-something for 2 lbs. Except that I do not want 2 lbs, nor do I want to weigh that stuff to get 1 lb. I'll be going to Ace tomorrow for a 1 lb tin of their stuff.
Just under 2 cups for a pound of lye by my scale.
You won't have much of a bath with 4 or 5 gallons of water, better to double it for more cubic feet of cleaning space. I run water to lye 4 gallons to 1 pound and use a large rubbermaid container - even then it won't handle larger pieces.