The problem with the tube fare this is that the further out, the harder it gets. I live in zone 6 so my fare is around £2200, but commuting 5 days a week, 36 miles RT is hard, and if I dont do it at least twice a week, by the time I have paid single fares, I may as well bought a travelcard.
I also live in Zone 6 and also have a similar length cycle commute.
Your body soon get's used to the daily ride and distance.