Buy 3 Get 1 Free on Funny T-shirts

We are running a special deal throughout September and October across our whole store - Buy 3 T-shirts, Get 1 Free. To spell it out, when you buy any 3 T-shirts, you will get a 4th one free. The lowest priced item is free and the discount is automatically applied at the checkout. The offer expires on 31st October 2009.