London King's Cross
Durham and stops in between those.
If it's anything like last time, if you get in early, there are LOTS of £5 tickets even on peak time trains. Not much info on Virgin East Coast site yet but more info here: http://www.birminghammail.co.uk/whats-on/whats-on-news/virgin-trains-launch-black-friday-12206899.
Note this is EAST COAST not WEST COAST so you can't go from Manchester, Birmingham, Preston etc. You could always book this say Leeds to London for £5 and a Manchester Victoria to Leeds for £3 (£2 or less with railcard) to connect to it as long as you leave the minimum connection time you're covered in case of delay.