In this context, appraisal refers to the decisions that archivists and librarians make about which parts of a collection have research value and which do not. We try to document these decisions so that researchers understand how collections came to us, what may have been removed, and how we made the determinations that we did.
We cannot answer questions about the monetary value of our (or others’) collections. If you are looking for this kind of help, a web search will return lists of professional appraisers.