It's so easy to forget that your salary is not everybody's salary. In Italy (a first world country afaik) a post doc makes a grand total of about 30 euros per day. An assistant professor probably around 45, which is similar to the entry salary of a software engineer. If you subtract food, housing and transportation, that $100 book starts looking very (very) expensive.
For a large fraction of the world's population time is not money...