If they are not willing to break these rates down then you could assess it yourself using what you consider to be open market rates (or threaten to do this and see if it gets a different reaction to being more willing to show evidence).
They are obliged to break the quote down in sufficient detail to allow you to decide whether it is the right cost, otherwise you have the right to assess it yourself if you don't think it has been assessed correctly (in accordance with the contract).
They are obliged to break the quote down in sufficient detail to allow you to decide whether it is the right cost, otherwise you have the right to assess it yourself if you don't think it has been assessed correctly (in accordance with the contract).