Just use the Drop down box to Select the Characters you want, Once you have added 4 Characters to your basket the cost will reduce to the Equivalent of the Cost of 3 characters.
Lego minifigures are fun to collect and the Series 18 set is particularly good. It contains a really good variety of characters including a highly collectible policeman character based on an original design from 1978. Highly recommend this set to any Lego fan.