Its a pity Zen, I've backed 45 projects on Kickstarter, all for $100 us each or significantly more... but in every case, at a physical reward tier. I have over 30 shadowrun books in pdf form along which I have yet to read, let along a cwap load more. So I only back at the physical reward level.
Charge a flat fee which is reasonable, maybe around $10 us each for international. Its just a novel, so shouldnt be tooooooo heavy. Do some calculations, see how that works out for you.