Single or return? Any railcards or are you eligible for any?
If it's just a single journey then my feeling is a simple split in London will probably be a good bet - this allows you to make use of FGW's sensible pricing of pricing of singles from London. Further splits will undermine this so unlikely to be of use here. I've not looked into creative routeings - nothing obvious comes to mind and I'd not suggest anything too wacky.
Through fares - Stansted Airport (SSD) - Bridgend (BGN):
Super Off Peak Single - £79.50
Super Off Peak Single - £80.50
Split in London:
SSD-London Anytime Single: £22.50
Oyster PAYG to cross London: £2.00
London-BGN Super Off Peak Single: £42.00
Total: £66.50
If you don't have an Oyster card, I'd advise purchasing a ticket from Stansted to Acton Main Line instead, this is £24.90 and will cover your Tube journey across London to Paddington. The Stansted-London leg is valid at any time, obviously, and the Paddington-Bridgend ticket has restriction
YW, depart between 10:10 and 15:01 and from 19:01.
If you held a
Network Railcard, it would be better to buy SSD-Didcot Parkway (DID) Anytime Single with the Network Railcard discount, plus DID-BGN Super Off Peak Single, totalling £58.20. Even if you live outside the South East, a Railcard could make savings even on a few trips around London.