Remove white spaces and letters from a string

Hi All,
I have a string which contains white spaces, characters, dollar sign and a number. From this string I would like to remove everything except the dollar amount. I tried different ways like using Indexof, String.Replace(). But nothing served my purpose.
If you have any idea of how to approach for the below problem, please let me know.
I highly appreciate your response.
Current input string= "$50 or more";
Desired output string = "$50";
...