CGC Census shows
149 graded comic books for Cerebus #1.
Whooping 6842 graded books for Hulk #181. Many raw grade copies are always selling on ebay everyday.
From 9.9 to 9.0, there are 1851 graded books for Hulk #181 included Qualified, SS and Restored.
There are only 2 at 9.4 and 4 at 9.0, 3 at 9.4 SS, 3 at 9.2 SS, 5 at 9.0 SS and one restored at 9.0. That is the total of 18.
How often do you see Cerebus #1 on eBay? Not very often. I sold one raw grade copy and three CGC copies of Cerebus #1 since 2009.
I sold Hulk #181 seven times since 2009. Right now, it is too expensive to buy Hulk #181 at any grade - too many competitors are after it. MSC recently sold Hulk #181 1.0 for $375, 1.5 for $450 and 3.0 for $750.
I would afford Cerebus #1 because of the few competitors. I bought it for only $325 and got CGC 7.5 that was sold for $665 via Comiclink last year.
So few high grade Cerebus copies are hardest to get. You won't see them for a long time. I can understand why Overstreet gave Cerebus the high value over Hulk 181 because of rarity in high grade.
I have no problem to find Hulk #181 between 9.0 to 9.6 anywhere at anytime.