Amazon's 4-for-3 promotion on children's books (and other items)

Amazon has got some select children's books on a special 4-for-3 promotion:  buy any 4 eligible items and get the lowest-priced item free.  Here's one scenario:

• Elmo's Little Dreidel for $5.99
• Happy Hanukkah, Curious George for $7.99 
• The Count's Hanukkah Countdown (Shalom Sesame) for $6.95 
• Hershel and the Hanukkah Goblins for $7.99

The total on these four children's Chanukah books is $28.92. But since they are part of the 4-for-3 promotion, the cost of least expensive one, Elmo's Little Dreidel, drops off, and your total cost is reduced down to $22.93, or an average of $5.73 per book!