Any quote should always say specifically whether VAT is included or excluded. Make sure this is in writing.
In my view the practice some solicitors still adopt of charging these fees as a % of the estate value is potentially very unfair & I would never be happy to accept it. This is because it is perfectly possible to have a valuable estate which is extremely simple to deal with, or to have a small one which is quite complex & time consuming.
For example, if the main asset is a house worth £300,000 & the only other items in the estate are a few bank or building society deposits the work will be very straightforward & yet a % fee is charged on the lot - including the house value. (Remember this does not include any fee for conveyancing work if the solicitor also acts in sale of the house - that is a quite separate instruction with its own fee.)
The problem you have is that the solicitor is an executor & that rather limits your options. Nonetheless it would certainly be worth negotiating - including asking for a quote on an hourly rate basis if you feel the estate is of the kind outlined above.