Exeter Train Advice - read if on a budget!
Rather than using Trainsplit, buy these tickets from GWR website / app, or Oxford station ticket office:
Oxford - Bristol Temple Meads, Off Peak Day Return (not via Reading) £32.10
Bristol temple Meads - Taunton, Off Peak Day Return £17.30
Taunton - St James Park (Exeter), Off peak Day Return £15.90
Total = £65.30 (no fees)
St James Park station is next to the ground and a ticket from Taunton is the same price as to Exeter St Davids.