Dynamic percentage based on attributes applied

Ok great, the formatting must have been the elusive element.

Doing some quick maths:

208764.42 / 37968039.17 = 0.005498425.  As a percentage that should be 0.54%.  So that means you are correct in that its 100 times too small, plus the number itself is wrong.

Lets create 2 more measures. 

Numerator = SUM('YourTable'[SumActualCost])
Denominator = SUM('YourTable'[Total Cost])

Bring those into the matix next.  I'm curious what that comes up with.

For the reason the reason it doesn't add to 100%, i believe My error is with Total Cost.  Instead of SUM for the Denominator, we should use MAX instead.  This is because you don't actually want to sum up that column.

No definately not, thats not necessary.  Does your formula now look like?

Simple % = DIVIDE(
     [Numerator],
     [Denominator]
)

Remembering Numerator and Denominator are measures, so we can call them directly in our new Measure.