I'm guessing without seeing what your underlying data looks like, but I assume you are saying you want to "swap measures" based on the comparison of each record's [Unit Year] compared to today...
So instead of creating a "lookup" as you put it, I think you just have to build a calculated field that uses an if statement against the [Unit Year] to determine which field to use as the measure field.
For example, I am assuming you have 10 different columns that show CostYear1, CostYear2, CostYear3--each being a measure.
Create your [MeasureToUse] field as:
IF YEAR(TODAY())-[Unit Year] = 1 THEN [CostYear1]
ELSEIF YEAR(TODAY())-[Unit Year] = 2 THEN [CostYear2]
ELSEIF YEAR(TODAY())-[Unit Year] = 3 THEN [CostYear3] ...
Does that help? If not, could you post a packaged workbook with your example?