How much would it cost to change a cambelt on a P reg Rover 600?

I am in the UK Norfolk, I have a rover 600 2.0 P reg I am trying to find out the cost to replace the cambelt can anyone help?How much would it cost to change a cambelt on a P reg Rover 600?get estimate from garage what the cost would be prior to having the job done , probably cost around the100 mark