Do you know of any model RR clubs in your area? You could donate the collection to them, and let them do all the work. A larger group should have some knowlegable modelers who could give you a good idea of the value of the collection. The donation could be considered a tax deductable contribution. The key is to be sure that they are a registered not-for-profit organization, and they should provide you with the proper documentation for the tax people - maybe BigRusty can comment on that as well.
I volunteer with the Modelers Group at the Boothbay Railway Village in Maine. We have accepted a number of donations over the years that we use to fund the new layout we are building. I am not pushing or offering our group’s services; just letting you know about another alternative.