Timetable world (< click the link) shows a price of 64 Shillings (so £3 4s) for an ordinary single journey in second class a few years back in 1965. Under 14s were half price and under 3 were free. So whilst not exactly what you need I guess it may be a ballpark figure with no doubt increases over the years to 1970. So maybe about 70 Shillings ?
Of course there may have been special returns available, weekend returns, some type of excursion tickets or other inclusive fares to bring the cost down a little, a few years before my time I'm afraid.
Hope this helps, if only a little