There is a hilton and a travel lodge just off junction 21.
Alternatively the is an ETap hotel which is £26 a night for the room and can accomodate 3 people so uber cheap if you can find people to share with.
http://maps.google.co.uk/maps?f=d&so...,1.223602&z=10
The ETap is at position A, roughly 15 minutes from Mallory