qryFCRReasonsTotal gives you one record, and one field in that record, correct? If so, then rather than using that query as a subquery, just put it without any relationship into the top area of the query grid where tables and queries normally go. Then just reference the [Total Cost] field from that total query in the calculation where needed. Here is the SQL from a test query that I just build and tested. It worked.
SELECT DateText.Field1, [Field1]/[TotalCost] AS WeightedValue FROM DateText, qryTotalCost;