Hobo Ninja offers this Doctor Who-Inspired Police Box T-Shirt for $9.99. Coupon code "IAMTHETARDIS" cuts it to $5.99. With free shipping, that's $4 under yesterday's mention and the lowest total price we've seen. (It's a current price low by $4.) It's available in sizes S to XL. Deal ends October 22.
Note that size XXL is available for an additional 99 cents and size 3XL for $1.99 more.