Main text: Evolutionary Analysis, 4th ed. by Scott Freeman and Jon C. Herron. Publisher is Pearson/Prentice Hall. A 3rd edition would be ok too.
Supplemental text: Evolution: the triumph of an idea by Carl Zimmer. ISBN 0061138401. Paperback.
You can probably pick up used copies of either book online.
Amazon.com (the used section) and abebooks.com are both likely sources if you want to try to pick up an inexpensive copy.