You're talking about 3 different things here:
The CPL is valid 5 years and the cost of renewing is in the CAA scheme of charges.
The MEP class rating is valid for one year as is the instrument rating. Revalidating both in an aeroplane will take around 1 hr 30 mins and the examiner will charge you his fee.
If you do just the MEP class rating in the aeroplane it will take around 40 mins. The IR in an FNPT will take around 1:20.