Have you looked at going to Doncaster/Sheffield and then across to Huddersfield? In my experience some of the cheapest fares can be obtained to get to Doncaster. Depends how bothered you are about getting their quickly and how early/late you are prepared to get up/go to bed. EG you can go to Doncaster for £11 leaving Kings Cross at 08.11, arriving at Doncaster at 12.03. You can get back to London for £11 too, but it gets in just before midnight. But for £22, plus whatever the connection costs, I wouldn't care compared to £85
Worth looking at anyway.