Well... using VT's website, I could see this available for £39. See below:
:
Journey Summary
Outward
From: Manchester Piccadilly (MAN)
To: London Euston (EUS) Departs: 11:35 27 Nov
Arrives: 13:42 27 Nov 0 changes Ticket Type : Advance Single £28.00 This price last checked 1 hour ago
Return
From: London Euston (EUS)
To: Manchester Piccadilly (MAN) Departs: 21:50 29 Nov
Arrives: 00:58 30 Nov 0 changes Ticket Type : Advance Single £11.00 This price last checked 1 hour ago
£39.00
Where did you get £99 each way??? Personally, if it was any more than £40, I'd get the coach. It doesn't take as long as you think if you bring a few magazines. I've done London to Newcastle countless times by coach in the past and it's bearable. Or you could get a coach down, with a train return - which I found for £11. Megabus should be around £8-9 so you could get a return for less than £20.