Using rough estimates.
They're are at least 350,000 owners on Steam, according to SteamSpy. Given the Kickstarter achievement (14.8% at time of writing), that suggests 52,000 of 77,000 backers activated on Steam. That's a fairly believable number, so I have no reason to doubt them. So, we're to drop that to 300,000 in sales. Also, backers like Sensuki bought like 20 keys to fence for 20 dollars a piece, so I'm going to drop 10% (30,000) because cranberries.
However, historical trends (using mostly the Witcher franchise as an example, but also other games) indicate that 20% of early sales for an RPG of this type should have occurred on all of the other digital retailers, 16% from GOG and 4% from everyone else. So we're going to say 60,000-80,000 copies have been sold outside of Steam, tacking on some additional sales because of its association with the well established Infinity Engine/Forgotten Realms metaseries on GOG.
That's brings us to about 330,000-350,000. Multiply by $45 and you get about $15,000,000.
Steam and everyone else get 30% right away. Good-bye 4.5 million.
That leaves 11.5 million. Let's assume Paradox gets half and Obsidian gets half.
5.75 million each.
Taxes on software entertainment companies in the U.S. are about 14% state and federal.
So you lose 805,000, thereabouts.
Leaving just shy of $5,000,000.
However, a few tens of thousands of those sales were royal edition and/or upgrades, which would explain revenue remaining competitive with GTA5 for a week despite such a hugely lopsided difference in sales.
So we get over 5,000,000.