We envisioned the $90 price for the book from the start - it was planned as a huge resource - the biggest on the planet which we're happy to report has been achieved now.
We launched at $75 for the first month, but then Covid hit and we decided to keep the lower price for a while longer. The deadline was moved twice already, but the latest update also marked us exceeding 500 pages, so I decided that it's finally time.
It's bigger than most courses on UI design and a lot less expensive :)