Fees for charity accounts

A charity has approached me to prepare their annual accounts (as an independent examiner) and complete the charity commissioners annual return and the gift aid returns.

I'm not sure exactly what will be involved but would like to give a fixed fee quote and a discount as it is a charity.

Anyone have any ideas?

On the basis of two gift aid returns per year plus the accounts and annual return I was thinking £600 discounted to £300.

What do people think?
Dave Martin