Anybody who 'guarantees' you a MEP rating in 6 hours should have their training approval withdrawn.
I see you are based in Fife, and I am not familiar with any schools in that part of the world. On the CAA website you can find a list with all approved training organisations offering MEP training, that might be a good starting point.
Approved Schools
Going rates: between 200 and 250 per hour for dual training. Another hour or so for the test and an examiners fee. About £1500 as a minimum I would say.
When comparing prices it is important to check landing fees at your training airfield. These can sometimes be over £15 per T&G, which quickly starts to add up.
Cheers