I've been meaning to get this book on Amazon for a while and it has been hovering around the $10 mark. I checked last night and it was at $2.99, an 81% discount.
I'm pretty confident it hasn't been this cheap before and I know that when I saw this price the bargain jumped out at me. I hope there's others who've been wanting to read this great book - because now is your moment!
EDIT: The $2.99 price is only available in the US Amazon store if your Kindle is registered to the US store. It's still $10.03 in the Australian store. :(
EDIT2: A few commenters seem to be seeing a different price. The $2.99 appears on the US Amazon store for me, but that's logged in with a US-based account. This may not work for the AUS store or for the US store under certain conditions.
Shows at around $10 for each (paperback and Kindle) edition for me.