Ok let's have a crack at this and estimate using Fermi's method for the US only. (All numbers are pulled out of my ****hole)
323 Million people in the US
Let's say 1 in 1000 people collect comics so 323,000 comic collectors in the US. (Given that Batman can sell 100,000 copies that is probably not unreasonable)
Top 1% of US Income ($456,000 annually) 3230 comic collectors in the 1% income bracket.
1 in 10 Comic collectors may be art collectors (it is more niche) 323 people.
People able to spend a million a year let's say 10% so 32 people.
There were 13 people in the Cabal photo, and the one taking the photo........