Have a look at the stops in between. Try e.g. London to Crewe, then Crewe to Stockport as separate tickets. That can save you tons, especially if you can be a bit flexible with time.
We've just got our Everton travel for £36+tube each doing that, using a 2 together and splitting the London-Liverpool leg at Crewe.
It can be a bit of a faff getting the timings of the cheaper tickets to match up, sometimes it works, sometimes it doesn't. What time do you need to be in Stockport?
An example for one adult without railcard, tonight's prices:
Sat 24th Aug
Euston 08:40 - 10:56 Crewe £10.50
Crewe 11.10 - 11:35 Stockport £14.40
Sun 25th Aug
Stockport 11:17 - 11:52 Crewe £3.40
Crewe 12:13 - 14:29 Euston £14.60
Total £42.90 per adult, plus travel up to London & back from wherever you're going from. And cheaper still if you have a railcard.
You can also save on the London leg by going Brighton - St Pancras on the Thameslink, takes a bit longer but only about £15 for a single. 10-15 min walk to Euston if you're able and the weather's ok, or tube from Kings Cross if not. If you're starting from Lewes then obviously it means getting into Brighton first, so you might be happier paying the extra and going quick to Victoria instead.
Just some examples, might not suit your timings or who you're travelling with, but it may be worth a look while there are still advances available.
Either way, hope you find what works for you.
