I bet 700 was the last sale which was a long time ago. All grades of Cerebus 1 has been going up significantly since Covid hit in 2020. Early on during the pandemic, every copy was wiped off the market. Due to it's low print run, only a few copies trickle out since that time. The most recent sale of $7200 for the 7.5 is probably more reflective of the current market, though obviously at the upper end.
while Cerebus 1 doesn't have the recognition of Marvel bronze keys, I think it will likely maintain it's price point due to it's historical significance and rarity marking the rise of Independent comic creators (showing that these books could actually be popular) and paving the way for TMNT, Image comics, etc. It's an important key in the history of comics.
Congrats on picking up a copy. Is it authentic? What grade is it?