My big block billet price is like $120 for a 24" x 20" x 96"
My single sheet price is about $30 per 24" x 96" in either 3.5" or 4" thickness
I could do this stuff at my house with the single sheets because they’d be easier to store and all…
I guess another question is, is it harder to cut rocker into a sheet than out of a big billet?
It depends. If you’ve got enough space in the sheet to fit your rocker, the wire doesn’t seem to care if there’s 1/4" of foam between it & air, or 4 feet. But if you’re fitting rocker in a 3 or 4" sheet, you’re either making a fish or bending in more with a bag later 
I recut all my hotwire rocker/thickness guides to be completely flat on the deck. I press in rocker when bagging on the bottom skin. I get a heck of a lot more pieces per block that way Sabs has done some testing which shows that a blank bent & set to a skin remains under a bit of tension (makes sense_yeah?) and adds to the flex-return component of performance.