Rapunzel's Revenge by Shannon Hale has dropped from $7.99 temporarily to $3.50. I haven't seen this one on sale before. It's a graphic novel so reading on an ereader may vary by person, but it's definitely a worthwhile read and well worth the full price let alone the sale price.
Rapunzel escapes her tower-prison all on her own, only to discover a world beyond what she'd ever known before. Determined to rescue her real mother and to seek revenge on her kidnapper would-be mother, Rapunzel and her very long braids team up with Jack (of Beanstalk fame) and together they perform daring deeds and rescues all over the western landscape, eventually winning the justice they so well deserve.