You can do it this with two replace’s
//let stw be "John Smith $100,000.00 M"
sb_trim = Regex.Replace(stw, @"\s+\$|\s+(?=\w+$)", ",");
//sb_trim becomes "John Smith,100,000.00,M"
sb_trim = Regex.Replace(sb_trim, @"(?<=\d),(?=\d)|[.]0+(?=,)", "");
//sb_trim becomes "John Smith,100000,M"
sw.WriteLine(sb_trim);