I have no knowledge about the cost of making either hood but with the financial resources of GM and the desire to give the Camaro racer the parts deemed necessary to be competitive and win, I'm sure they didn't sweat the cost in the least.
Regarding the weight of the hoods, Frank relays the following to me...
"I never weighed the hoods, but I remember the fiberglass hood was definitely lighter than the steel hood. Wayne Guinn talks of the weight savings in his 'Camaro Untold Secrets' book on page 98: fiberglass hood 35 pounds vs. steel hood 50 pounds; and then factor in hood springs 8 pounds, ZL2 hood plenum valve 5 pounds, upper and lower latch mechanisims 2 pounds = 30 pounds weight reduction."