Amazon has DC Super Friends: Flying High (Step into Reading Paperback Book) for $1.93 with free shipping on $25+ or with Prime. A classic at our house. Others on sale:

• Sing Your Song! (Nella the Princess Knight) for $1.48 (temporarily out of stock but orderable)
  
• Mulan Is Loyal/Merida Is Brave for $1.78 (ships in 1 to 3 weeks)
  
• Driven to Win! (Disney/Pixar Cars 3) for $1.48