Most prices at those shops are partially based on fame, i know i dind't get thos prices i got lower cuz i've done sooo much questing its not even funny!
The only ones he sells on a regular basis are Cure III, Dispel, Protect IV and Protectra IV. The rest are available only if Windhurst is #1 in conquest
That's an impossible question if you are from Diabolos. I've been playing for 2 years and Bastok has come in first 3 times. 3 times!! =) Anyway, as a lvl 34 paladin i found buying from this guy was very useful, as Banish2 couldn't be found in any AH.