Converting a rank/count/value apportionment formula from Excel to BI

I have a formula in Excel which takes a total cost value and apportions it against various grades, which are ranked.  The quantity of a particular ranking can vary by month and by factor (shown here as Colour) but the total value will be a set figure each month.  For example:

Those formulas:

Ranking formula:		    COUNTIF($B$2:$B$10,"<="&B2)
Apportionment formula:		$F$1*(COUNTIF($B$2:$B$11,"<="&B2)/SUM(C$2:C$11))

I can't seem to translate this to BI however.  Essentially I need to 1) count the number of instances of a given grade in a single month/month end, 2) sum the count of (1)) for a given month, then divide 1) by 2).  It seems like it should be simple but I can't seem to get a grip on the formula flow in DAX and my brain is melting as a result.

If I have the following data:

Month End	Colour	Grade	COUNTIF	As %
31/12/2023	Blue	A	1	5%
31/12/2023	Blue	B	2	11%
31/12/2023	Blue	B	2	11%
31/12/2023	Blue	C	2	11%
31/12/2023	Red	    C	2	11%
31/12/2023	Yellow	D	1	5%
31/12/2023	Green	E	3	16%
31/12/2023	Orange	E	3	16%
31/12/2023	Purple	E	3	16%

Then  I'd like to be able to allocate 5% of the total costs against an A grade, ~21% against a B grade, ~21% against C, 5% against D and ~48% against E.

I can't seem to replicate the combination of COUNTIF, percentage over a set of criteria (grade and month end), and grouping those values.  Actual grouping in Power Query didn't help unfortunately.  Is there something more simple I'm missing here?