Amazon offers Prime members the Gerber Baby Boys' or Girls' Hooded Cardigan & Pant Sets in various styles (Boys' Blue Bear pictured) for $6.99 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $5.48.) That's $8 off list and very cheap for a name brand set. They're available in sizes from newborn to 24 months, although not in all size/style combinations.
Orders placed by December 22 with Prime and non-Prime orders placed by December 19 are guaranteed to arrive by Christmas.