Sometimes it can prove more cost-effective to combine 2 different single tickets instead of booking a standard return.
Make sure you do try this, especially when travelling off-peak dates or times, as the savings can prove to be significant.
It is however very important to ensure that when doing this you do check the individual ticket type terms and conditions very closely, as 'Specials' & 'One Ways' often have specific restrictionsand are rarely changeable or amendable.