$20 for 40lbs is 50cents a pound, which is not terribly bad for off season pricing. 25 cents a pound is the gold standard for Memorial Day, July 4th, and Labor Day sales on plain ol' K.
The sales last year at Lowes and Home Depot were for smaller bags than those 20 pounders.... (they were 13.9lb bags for 6.97, I believe not 5.97) That works out to 25cents per lb.
Your best bet is to buy a year's worth every Memorial Day.
My recollection was that the Costco price for the K-Comp was about 60cents / pound. I gotta stock up on that this year. Better stuff, and less residual ash in smokers.
My rule of thumb for prices per pound: 25c for K; 55c for K-Comp; under $1 for lump. Good Lump is hard to find (cheap) in Chicago.