Opportunities.Proposals

We don't track individual expenses with proposals. (We tend to track totals for the Major Gifts program as a whole, or by fundraiser, rather than itemizing to a specific donor.) The only place I can see to do this would be under the Custom fields of the Proposal/Opportunity itself. You could create a dropdown table for expense type with a dollar value in Comments. However, you would then need to export to csv in order to tally up your expenses or run any sort of analysis from them.