Sorel offers its Sorel Women's Cozy Cate Waterproof Boots in Peatmoss, Fawn, or Black, for $69.98 plus $6 for shipping. That's the lowest total price we could find by $22. They're available in sizes 5 to 12, although not in all size/color combinations.
REI offers the Bogs Kids' Digital Camo Rain Boots in Black or Olive for $34.73. Opt for in-store pickup to avoid the $5.99 shipping fee. That's $15 off and the lowest price we could find. They're available in sizes from little kids' 7 to big kids' 6.