Regular expression only working in command prompt, not as variable

I want to check if a file name contains ~$ (tilde and dollar) as the first two characters, because then it's an Office backup file. That should be the following regular expression:  ^\x7E\x24

When I create a c# program where I have to type in the regular expression in the command prompt like this it works fine:
Enter regular expression: ^\x7E\x24
Enter input for comparison: ~$rbar i Nordic.doc

However, when I use the same regular expression as a string variable in a c# program where fi is FileInfo, it doesn't work:
string reTildeDollar = @"^\x7E\x24";
if (Regex.IsMatch(reTildeDollar, fi.Name))
                {
                    Console.WriteLine("Office backup file - will not be copied");
                }
                else
                {
                    this.CopyToSharepoint(currentDir.FullName,fi.Name, fi.LastWriteTime);
                }

Can anybody tell me why? (and yes, some of the files start with ~$)