create an underline equal to number of characters in cell below

I want to underline a number but I want the number of characters underlined to be equal to the number of characters in the cell below.

For example, I have data in cells A1:A5 as follows:
20,000
500
500
50
21,050

If I underline the 50 the result is:
20,000
500
500
50
__
21,050

If I put a line in the cell the result is:
20,000
500
500
50
________
21,050

The desired result is:
20,000
500
500
50
______
21,050

Is there a way to do this? Example attached if needed. Thanks for any comments.

it's not a good idea to store numbers as text for purely cosmetic reasons.

Possibly the best you will get is,select the cell, then Format > Format Cells ...
Font > Underline:= Double Accounting
Border >Top