It will be cheaper to buy a single up and another single back since up will be peak and down will be offpeak or super offpeak. Depending on how long in advance you know the dates there may be advance tickets available.
Note that at the moment GWR▸ will allow advance tickets to be changed to a different train or type.
At the moment if you travelled on 14/15 Januaey the cost would be:
Up:
06:25 Standard return £281.80
06:25 Advance single £62.10
06:25 Anytime single £140.90
Down:
17:36 Advance single £62.10
18:04 Advance single £74:50
18:04 Off peak single £82.40
19:04 Advance single £36:40
19:04 Super offpeak single £59:70
It will also be cheaper if you split the ticket and their are specialists on this site who can advise you.
This is fantastic. Thank you. I will use this as the basis for some more searching. I am pretty flexible on the time of day I travel so it’s good to know that there is a good spread of options and price points.