Cyfr,
Megabus are doing 2 seats for £10 each way Manchester to London
megabus.com - low cost intercity travel in the UK
IIRC the first bus from accy is ~6:30 so you might need to get a lift into M/c (speak nicely to your friendly local techie and I could drop you off, You can make your own way home though
That should give you return journey for ~£13 each