His probably has a two-page inscription as well!
As for price, as this is one of my two or three favorite Buk works, I might go as high as half the current BIN. Maybe. Considering an unsigned copy is about $600, with the drawing, comment and signature, $1,000 doesn't seem unreasonable. They'll probably hold out for twice that for years to come...
Some useless trivia - although ATAITWAM came out after Confessions of a Man..., in the original ...Assholes..., Buk's character isn't Henry Chinaski, it's Henry Charles Puchinski Jr. This is the only edit made that I have seen when it was reprinted in South of No North.