Probably $50 - $60 for the colossal red dragon from Wizards several years back. My wife accidentally locked me out of the house one Saturday morning while she and her mom went shopping, and she let me get the dragon to make it up to me.
My family used to do that to me all the time when I was younger living with them. In no time at all I learned all sorts of ways to break my way back in. :p Though I can't say I ever got any reward out of it...
As far as minis, I'm with several others in the thread who spent a disgusting amount on Warhammer Fantasy and Warhammer 40k minis (most expensive probably being one of the more elaborate pewter Tyranid models or perhaps some type of Eldar vehicle). Thinking back, I also probably spent a good deal on Mage Knight, although that's more quantity-related.