Hobo Ninja offers The Walking Dead Walkers In A Winter Wonderland Ugly Christmas Sweater T-Shirt for $9.99. Coupon code "WINTERWALKERS" cuts it to $7.99. With free shipping, that's $2 off list and the lowest total price we could find. It's available in sizes S to XL.
Note that size XXL is available for $1.89 more, and 3XL for an additional $2.49.