Generac NG generator

Considering buying a Generac 8Kw natural gas generator. What would it cost me to run for 24 hours at half load with a Nat Gas price of .63 per ccf? I am not sure how to do the math on this one. It will use 77 cu ft per hour at 1/2 load and around 139 cu ft per hr on full load. Thanks

1 CCF is 100 cu ft

$0.63 * 77 * 24 hr / 100 = $11.64 (half load)

At full load, it is about $21/day.