I think you are on the right track. If you want 100/3200 that would be the TOTAL ignoring all dimensions except the Org. Is that correct? I believe the syntax for that would be:
Sum(COST)/Sum(TOTAL <Organization> COST)
Did you try that already? One thing you could do is just try getting the denominator, so:
That should give you 3200 on all of the A lines.
Sum(TOTAL <Organization> COST)
EDIT: I attached a sample.
Totals.qvw 140.8 K