I won't guess the price, but the three routes that came to mind, i'll list the two most likely

Shirehampton - Bristol Temple Meads
Bristol Temple Meads - Birmingham New Street
Birmingham New Street - Tame Bridge Parkway
Tame Bridge Parkway - Wrexham General
If you did it this way, did you perhaps split the tickets at Bristol
TM▸ and Tame Bridge? Strangely enough a
FC▸ Return from Bristol TM to Tame Bridge Parkway is cheaper than a Birmingham New Street return, yet is valid via Birmingham New Street...

Unsure if the same applies to SC tickets
Another route that springs to mind and is rather scenic is:
Shirehampton - Bristol Temple Meads
Bristol Temple Meads - Newport (S Wales)
Newport (S Wales) - Shrewsbury
Shrewsbury - Banbury
Banbury - Reading
Reading - Bristol Temple Meads
Bristol Temple Meads - Shirehampton