using System;

using System.Text.RegularExpressions;

public class Program

{   

    public static void Main()

    {

        string plainTextValue = string.Empty;

        plainTextValue = "Pricing Obfuscation Test:\r\n $100, $ 100, $100.00, $ 100.00, $.10, $ .10, ($100), ($ 100), ( $100), (100), (100.00)";

        string output = Test(plainTextValue);

        Console.WriteLine(output);

    }

    private static readonly Regex Pattern = new Regex( @"[^\(\p{Sc}.*\)](\p{Sc}\s?[+-]?[0-9]{1,3}(?:,?[0-9])*(?:\.[0-9]{1,2})?|((\p{Sc}\s?)+\.[0-9]{2}))|\((\p{Sc}[^)]*)\)", RegexOptions.Compiled);

    private const string replaceValue = @"$___";

    private static string Test(string input)

    {

        return Pattern.Replace(input, match => { string newMatch = match.Groups[1].Value; return replaceValue; });

    }

}