I agree. Didn't realise that 3 of the planes would be free, and I already own the P51, so...
As much as I want to back the project, the $87 I pledged now seems like a lot when the incentive is only a couple of free books.
Edit: Yeah, I might do what Ron says above; to be honest, I'm already tempted to lower my pledge and wait for the free version (free Spitfire!) but that sort of attitude doesn't get kickstarter projects off the ground!