The price on Munki Munki Ladies' Flannel PJ Set Exclusive Costco Theme with Sock, has dropped to $15.99... These may not be the cheapest PJ's you can buy, but I own last year's print and they are very comfortable.
I bought these two days ago as a gift for a friend who is also a Costco-junkie and paid $22.99 I decided to order another pair for myself today and saw the price dropped to $15.99. I ordered mine and requested a price adjustment for the pair I bought two days ago. For comparison, I paid $19.99 for my set last year, and they did not include socks.
I didn't pay shipping fees and there is no sales tax on clothing in my state. $15.99 total