I'd love to come down for this, sounds like a really cool kind of ride and just the sort of thing I love ... but £80 for the cheapest train I can find is just killer. I'll keep searching for offers though, just in case
I have an ex Londoner mate, who does Stockport to London for meetings on a regular basis, he has discovered "anomalies" in the system, sometimes he gets a first class single in one direction for less than the equivalent part of a return. His logic is that First class comes with perks like food, drink and wifi that you would have to spend something on anyway. I've asked if he can share some more knowledge.
If you need accommodation and don't mind a bit of roughing it, I can provide an overnight stop given a bit of notice (to clear the bed of junk). If you like ethnic food you are well served in Croydon.UPDATE #1
Message from Mat my train travelling buddy:
£80 return sounds about right ... but try http://www.thetrainline.com
... and don't forget to book the bike as well, they insist on that these days. It's free, but they need to plan for it.
Try here http://www.farefinder.virgintrains.co.uk/
Manchester to Euston from £12.50 each way, if you don't mind a 4am departure or arriving back at midnight.