Once a week I have to go to London for the day (there and back in a single day).

Once I get into London, I have to get the tube. One journey to my destination and then later in the day one journey back to the train Station. It’s all Zone 1, very occasionally 2. Can be any day, including weekends.

It’s £13 for a return on the tube (I just buy a ticket from the machine at the tube station) which seems excessive to me - over £50 a month for just 8 journeys. Is there a cheaper plan available?