[SQL] Formatting a '$' dollar sign to an SQL Selection Statement with SUM() in it?

I'm trying to format a '$' dollar sign to column "c" which is the SUM of all rows of two other columns multiplied together. I first turn it into a character as follows:

SELECT TO_CHAR(SUM(a * b)) AS "c"
FROM table1;


which works fine, but when I format it by adding 'L9,999.99' formatter it gives an error:

SELECT TO_CHAR(SUM(a * b, 'L9,999.99') AS "c"
FROM table1;


So I tried doing a CAST:

SELECT TO_CHAR(CAST(SUM(a * b) AS NUMERIC(10,2)) AS "c"
FROM table1;


But nothing is working.

How can I add a '$' dollar sign to a column with a SUM() function using TO_CHAR and/or CAST?

For reference, my intended output is to turn:

C
10
10.05
11.50


into

C
$10
$10.05
$11.50

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