I would guess pillars of eternity currently sold about $9.000.000 - $10.000.000, excluding backers.
There are 77.000 backers (source opening screen)
+- 60% of them choose steam (source http://forums.obsidian.net/topic/71538-steam-vs-gog-redemption/)
19.3% of the people currently playing pillars of eternity on steam who are backers (source steam global achievements)
This means the rest bought the game instead of kickstarted it. With a price of $44.99 the nets about $8.500.000 on steam. Throw in some extra sales on GoG and the special editions, and you'd arrive at $9.000.000 - $10.000.000
I don't know which percentage goes back to the developer but I'd say it's a commercial success.