Target offers the Disney Frozen Girls' Anna Nightgown for $8.48 with free shipping. That's $7 under our September mention and the lowest total price we've seen. (It's also a current low by $16.) It's available in size 4 at this price; size 6 costs $9.98.
Walmart offers the Frozen Toddlers' Elsa Classic Halloween Costume for $6.97. Opt for in-store pickup to avoid the $4.97 shipping charge. That's the lowest price we could find by $10, although we saw it for $2 less a month ago. It's made of polyester and comes in size 2T only.