Well, I don't know exactly how you are passing the variables, but if it would work in a straight form then try this.
// Your submit button
<input type="button" name="Submit" value="Submit" onClick="functionname()">
//javascript that you would actually use to
//pas the information
function functionname(){
theform = document.formname;
//amountvalue is the name of the textbox
theform.amountvalue.value = theform.amountvalue.value * 100;
theform.submit();
}
That is a basic idea of what you can do using Javascript. You could also pass it a hidden value instead of switching the textbox value. Hope that helps.