I bought the following books from or through Amazon.com for a total of $71.85:
"Becoming a Graphic Designer: A Guide to Careers in Design"
Steven Heller; Paperback; $18.90
"Universal Principles of Design: 100 Ways to Enhance Usability, Influence Perception, Increase Appeal, Make Better Design Decisions, and Teach Through Design"
William Lidwell; Hardcover; $21.60
"Introducing Postmodernism, Third Edition (Introducing)"
Richard Appignanesi; Paperback; $10.36
Amazon.com total: $50.86
"Designing a Digital Portfolio (VOICES)"
Cynthia Baron; Paperback; $17.00, Shipping & Handling: $3.99
Textbooksnow total: $20.99
My choices were based on price though I only bought one used (which saved me about $4 dollars). I was a bit anxious when I started ordering but now that I am done I am relieved and happy that the cost wasn't higher.