Very subjective - I really like the inscription, so if you compare it to a signed manuscript at today's silly prices of $600 and up, I suppose the asking price isn't so bad. My take is chap, $400-$500, inscription, $400-$500. Max $1,000 - $800 would be a fair asking price for this for an ebay listing, as I see it.
I bought a nice copy of Assholes several months back (it's my favorite work of Buk's), but it really is just a $1.00 publication - it shows. This inscription makes a difference.