Counting occurrences of Record ID number for use in a calculated column

In my SQL Server db, I have a field that contains a record ID that is repeated on each line of a transaction.  Another field contains total cost for the associated transaction that is also repeated.  Within the Excel file from which the data is imported, I can use the following equation to create a new column from which I can then use SUMIFS to get the total cost (SUMIFS on the original yields total costs * the number of lines in which the amounts are repeated).  The Excel equation is =(SUMIFS(Cost column, ID column, ID number)/countifs(ID column,ID number))*(1/countifs(ID column,ID number).  Here is a sample from Excel

Equation
=(SUMIFS(Q:Q,P:P,P7)/COUNTIFS(P:P,P7))*(1/COUNTIFS(P:P,P7))
ID Number	Cost	Calc Column	Trx Total	Proof
12345	1,250.00	416.67	1250	-
12345	1,250.00	416.67	1250	-
12345	1,250.00	416.67	1250	-
67891	1,422.00	284.40	1422	-
67891	1,422.00	284.40	1422	-
67891	1,422.00	284.40	1422	-
67891	1,422.00	284.40	1422	-
67891	1,422.00	284.40	1422	-

 

I would like to add a calculated column to the table that accomplishes the same thing.  Each row would then produce a fraction of the total that will add up to the correct amount when aggregated at the ID number level.

 

Is there a way to pass the number of times a field includes a particular result (ID number), to the calculation?