As one of its daily deals, ThatDailyDeal offers this Unhappy T-Rex T-Shirt
in Green for $5.99
for shipping. That's the lowest total price we could find for such a shirt by $12, although we saw it for a buck less in our June mention. It's available in sizes S to XL. Deal ends October 18.
Note that size XXL is available for an extra 99 cents, and size 3XL for an additional $1.99.