Oyster PAYG is not magic. Introducing it does not automatically reduce fares – the fares are set by whoever is running the trains, and to some extent the law. Writing to your MP to ask him/her to get fares reduced is asking directly for what you want. Introducing Oyster PAYG would increase convenience, but that’s not your primary aim – ask for what you actually want.
Let’s hope that ITSO smart cards and/or contactless will be introduced soon. The former is conceptually like Oyster and both work by swiping the card to open the gates, but the *technology* does not determine the fares.