I figured with people selling iOS games that take months of development for $0.99, an eBook shouldn't be much more expensive than that… Plus my main target for this eBook is hackers and entrepreneurs, and since design is not their main field I wanted to make it as easy as possible for them to give the eBook a try.

And I agree that a $1.99-a-course tutorial marketplace would be very cool. Seems like there's already a lot of startups in this space (Skillshare, Udacity, Khan Academy…?)