Probate solicitors usually don't give a quote until they have been given details of all of the assets, including valuations. This is standard practice. The value of the estate determines the court stamp duty on the application which is scaled, and the details of the assets will determine the amount of work involved. It is different from other legal work, where it is easier to quote up front.
In this case of two assets a house and 5 acres surely renouncing is the legal option and that cost has nothing to do with the value of the 2 assets?
Also if they just did nothing and left everything as it is right now would that be a problem when the mother died?