To convert a varchar to currency, the recommended practice is to do the formatting in the front end.
However if that option is not available to you, you can use the following T-SQL code to do the formatting. In the code shown below, we are converting varchar into US Dollar currency.
DECLARE @t TABLE(amount decimal(12,2))
INSERT INTO @t
SELECT 27450 union all
SELECT 2841.2 union all
SELECT 8786723.62 union all
SELECT amount,'$'+ CONVERT(varchar(100),
CAST(amount as money),1) as converted_amount
Note : The value must be converted to money datatype before the formatting