C# - Best Way Of Validating / Creating A Number Only Text - Box?

I am wanting to have a numbers/currency only textbox control. So basically it should accept this kind of input

$123
523,100
$12.50
85.59

and convert this to

123
523100
12.50
85.59

and should not accept this input

F12
309$2342
,102

I have looked at validator controls but I would like to this conversion/checking completely from the client side. What would be the best way of doing this? I also would like a clientside error(message box or something) popped up if they try to enter invalid data and prevent them from leaving the bad data in the textbox. and then when they get out of focus of the textbox it automatically converts the data into a flat number from the client side.