There is currently an extra 10% off on top of all current reductions so the four shirts for £100 offer becomes £90 and then adding the 10% discount code 11WED1 takes this down to £81. Delivery is £3.95.
Quidco at 10% is available. If this includes the delivery price then it should be possible to receive £8.50 back, so the effective price paid would be £76.45, i.e. £19.11 per shirt.