Kmart is having some hot clearance deals right now. I found Joe Boxer footie pajamas (what do you call them?) for as low as $3.59, with decent size and color selection still available. Plenty to choose from for both boys and girls.
Just go to the Kmart website. The clearance banner is right there in front of you, or, I went in via the left-hand side bar. Clearance is down at the bottom. Orders of $59 or more are shipped for free, or you can do in-store pickup, which also will be free.