I kinda interpreted the $50 gc as "1/2 off $100"
1491 - Charles C. Mann
1776 - David McCullough
Adam Smith and teh Origins of American Enterprise - Roy C. Smith
Freakonomics - Steven D. Levitt
Parasite Rex - Carl Zimmer
The Physics of Superheroes - James Kakalios
A Short History of Nearly Everything - Bill Bryson
The Wealth of Nations - Adam Smith