For loads of cheap accommodation in London (with customer reviews, so that you can avoid anywhere nasty) try this website:
http://www.hostelworld.com/
Don't let the word 'hostel' in that URL put you off. Just enter your details and click the 'Search' button. Then place a tick alongside both 'Hotels' and 'Guesthouses' (in the 'Refine search' panel) and click 'Update'.
With most rail companies all of the bargain fares will have gone long ago. Use the National Rail website to see what's available:
http://www.nationalrail.co.uk/
(All available rail fares, with the possible exception of certain Megatrain fares, will be on that site).
'The Midlands' is a very large area though. If you're including the West Midlands in that, Virgin Trains (through the Megatrain site) still have off-peak tickets to and from London available for next week at a fiver each way. (Some tickets are even cheaper, at £3, while there are others available at £7):
From the North Midlands, there are tickets from Chesterfield available at £12.50 each way with Megatrain. From the East Midlands, they're also offering £12.50 each way (with a few tickets as low as £7) from Leicester. (There are also just a few cheap tickets available from Nottingham and Loughborough):
http://uk.megabus.com/default.aspx
(Yes, that really is the correct link. Don't let the word 'bus' put you off!)
Chris