DisneyStore takes up to 40% off its Halloween costumes and accessories. (Discount is reflected on product page.) That's the best Halloween discount we've seen from Disney Store this year. Shipping starts at $4.50, or get free shipping on orders of $75 or more via coupon code "SHIPTODAY". Sales tax is added where applicable.
A best bet is the Tangled Rapunzel Costume for Infants (pictured) for $22.12 plus $4.50 for shipping. It's $7 off and the lowest total price we could find. This costume is available in sizes 3-6 months through 3T.