1System.Globalization.NumberFormatInfo nfi = new System.Globalization.NumberFormatInfo();
2nfi.CurrencyDecimalDigits = 0;
3nfi.CurrencySymbol = "$";
4
5string result = String.Format(nfi,"{0:c}", value);
6
7// or just

8string result = "$ " + value.ToString("#,##0");