In USD the shirts are offered as four for $199. In GBP there is a four for £100 offer. There is also a 3 for £55 offer (requires an offer code).
With the exchange rate, it works out cheaper to use an offer code and put it through as GBP on the British version of the website or over the telephone. I would recommend placing an order over the phone - the offer codes are unreliable online (believe me, I know).
All of these offer codes can be used over the phone as 3 for £55. Phone up and quote one of these codes and you will get 3 for £55. This roughly works out as 3 for $71 with the current exchange rate.