How much are +3 to +4 INT Upgrade Tome going for these days? Also, where might these be likely to drop? I saw one drop in EE VoN6 and one in EE Cabal during a week in April, but none since.

I'll be using this on a character who has a +2 INT tome installed. I have a standalone +3 INT tome saved in the bank, and would be happy to help someone out by trading that to them for a +2 to +3 INT upgrade tome after I locate the other upgrade.