I'd rate the albums in this order of decreasing rarity (or increasing availability)
CHSIB (As rare as rocking horse shit)
WTTN (I see about a copy a month on ebay somewhere with varying end prices)
Bat III (US Red and European issues seem to have abuot the same availability now)
Bat II (seems that the standard vinyl is more rare than the picture disc)
The remainder are equally available although obviously there's more copies of Bat, Deadringer and Midnight floating around as they were truly released before the CD age kicked off.
They're all lovely though
