Again, the BTU per pound of different brands of charcoals is not the same as
indicated. I'm also assuming 10,000 BTU per hour, which is variable, based
on cooking temp, and the size of the cooking unit. I've been unable to find
anything about the ingredients of the Sam's Walmart charcoal, and the Trader
Joe's charcoall is claimed to be 100% hardwood plus cornstarch to bind and
lump is wood.
cost weight/lb cost/lb btu/lb cost/10,000 BTU
Comp to propane Cost/5 hrs Cost/10 hrs

20 lb Propane $20.00 20 $1.00 21000 $0.48
100.00% $2.38 $4.76

Sam's Choice $5.27 18 $0.29 9000 $0.33
68.31% $1.63 $3.25

Trader Joe's $6.95 18 $0.39 9000 $0.43
90.09% $2.15 $4.29

"Lump" Charcoal varies varies $0.55 9000 $0.61
128.33% $3.06 $6.11