As Ainsworth says, £10.65 for a single. A day return is £14.55, and to return within 1 month is £15.85. There are no "off peak" fares, these are all anytime fares. (The S&C doesn't have a peak!)
These fares seem reasonable. However splitting may reduce them further.
From Leeds to Settle the fares are £8.95 (single), £10.75 (day rtn), and £15.20 (rtn within 1 month) so it's not much more from Dewsbury, and it's certainly not cheaper to split at Leeds.
However when splitting you have to think of innovative ways round it. Not just splitting at the obvious places! In fact, if you look at the fares from Dewsbury, you can get some way toward Settle for only a few pence more than the price of going to Leeds, you can get as far as Keighley before the price starts to jump up.
Dewsbury - Keighley is £4.25 for an Off Peak day return (assuming you are travelling on a Saturday?) then Keighley - Settle is £5.30 for an Anytime day return. The total is £9.55 for a same day return.
This represents quite a decent saving of around a third off the price of the through ticket priced at £14.55 for a same day return.