static readonly Regex re = new Regex(@"\$(\w+)\$", RegexOptions.Compiled);
static void Main() {
    string input = @"Dear $name$, as of $date$ your balance is $amount$";

    var args = new Dictionary<string, string>(
        StringComparer.OrdinalIgnoreCase) {
            {"name", "Mr Smith"},
            {"date", "05 Aug 2009"},
            {"amount", ...