Not including kickstarters.
Used/out of print: Realms of Chaos: Lost and the Damned (it was like $110 at the time, so I guess that was a good investment). Still probably the prettiest game thing I own. Adrian Smith pencils, geez.
New: Veins of the Earth.
And I guess, if you collected expansions and subscriptions… I’ve spent a LOT of money of WoW.