Shell Programming and Scripting

I'm working with a set of files where I'm trying to remove a set of characters from specific fields. The files are comma-delimited, and the characters I want to remove include:
- open parentheses - (
- close parentheses - )
- space followed by a dollar sign - $

I don't want to remove every occurrence of these characters as they may occur in fields that I don't want to remove the data from.

How can I remove specific strings from specific fields, like the 4th or 5th fields in a .csv per the information provided above? Thanks much!

Code:

echo '1,2,3,($test1,test2),6' | awk 'BEGIN {FS=OFS=","} {gsub("[()$]", "", $4); gsub("[()$]", "", $5); print}'