Amazon has a ton of deals on boxed sets of children's books.
The Trouble Begins: A Box of Unfortunate Events, Books 1-3 (The Bad Beginning; The Reptile Room; The Wide Window) $8.58
Other notable deals include:
The Wrinkle in Time Quintet Boxed Set (A Wrinkle in Time, A Wind in the Door, A Swiftly Tilting Planet, Many Waters, An Acceptable Time) for $10.99
Weird But True Collector's Set (Boxed Set): 900 Outrageous Facts $7.66
Magic Tree House Boxed Set, Books 1-28 $53.67
Nancy Drew Mystery Stories Books 1-4 $10.23
Emily Winfield Martin's Dreamers Board Boxed Set $4.82
Anne of Green Gables, Complete 8-Book Box Set: Anne of Green Gables; Anne of the Island; Anne of Avonlea; Anne of Windy Poplar; Anne's House of ... Ingleside; Rainbow Valley; Rilla of Ingleside $15.34
Puppy Mudge Collector's Set: Puppy Mudge Finds a Friend; Puppy Mudge Has a Snack; Puppy Mudge Loves His Blanket; Puppy Mudge Takes a Bath; Puppy Mudge Wants to Play; Henry and Mudge: The First Book $6.76
Bink and Gollie: The Completely Marvelous Collection $6.40
Judy Blume's Fudge Box Set $12.78
The Judy Moody Uber-Awesome Collection: Books 1-9 $15.36
The Ramona Collection, Vol. 1: Beezus and Ramona / Ramona the Pest / Ramona the Brave / Ramona and Her Father [4 Book Box set] $7.39
And many, many, many more...