It really depends on if you're buying from Mark or the secondary market. There was a double page splash that just sold for $6,000 on splash page. To be honest, anything with a decent zombie on it is probably going to set you back at least $1,000, if not more depending on detail, who else is on the page, page significance, size of the OA, if it was pre-100, pre 48, post 114 w/ Stephen, etc.
If you're buying secondary market, it may be even higher. For a book with 100+ issues and zombies everywhere, there aren't really as many crazy zombie pages as you would think. Which is probably why it's been so good.