I have a used CS109 Textbook for sale for $40. The book is "A First Course in Probability" by Sheldon Ross, ISBN 9780136033134, and I think this is lower than the price for a used one on Amazon.

Available to pick up either in East Palo Alto where I live, or on campus whenever I make it over to campus. If you're taking the class this quarter, we can meet there instead. If interested, please send a message and I'll get back to you as soon as I can.