extern function Strip(VarName, NextURL) {
   VarName = URL.unescapeString(VarName);
   NextURL = URL.unescapeString(NextURL);

   var Unwanted = '$ @ !? darn';
   var Replace = '+';

   var v = WMLBrowser.getVar(VarName);
   if (! String.isEmpty(v)) {
      var n = String.elements(Unwanted, ' ');
      for (var i = 0; i < n; i++) {
         var u = String.elementAt(Unwanted, i, ' ');
         v = String.replace(v, u, Replace);
      }
   }

   WMLBrowser.setVar(VarName, v);
   WMLBrowser.go(NextURL);
}

And here's a driver WML deck to test it:

<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"
      "http://www.wapforum.org/DTD/wml_1_1.dtd">

<wml>
   <card>
      <p>
      Introduzca un valor:
      <input title="Value:" name="v" format="M*m"/>
      <br/>
      <a href="StripDollar.wmls#Strip('v','%23c2')">Enviar</a>
      </p>

      <do type="accept" label="Enviar">
         <go href="StripDollar.wmls#Strip('v','%23c2')"/>
      </do>
   </card>

   <card id="c2">
      <p>
      El valor correctamente es: $(v).
      <br/>
      <anchor>
         Repeat
         <prev>
            <setvar name="v" value=""/>
         </prev>
      </anchor>
      </p>

      <do type="prev">
         <prev>
            <setvar name="v" value=""/>
         </prev>
      </do>
   </card>
</wml>