Allow only numbers, decimal and major currency symbols

Hello,

The following line of code is for an input box that only allows the user to use numbers, decimals or "tba". How can I add to this so that it also allows some of the major currency symbols like the Euro symbol, the pound and $...

if (strtolower($cost) != 'tba') {
		if (!ereg("^([0-9]+|[0-9]{1,3}(,[0-9]{3})*)(\.[0-9]{1,2})?$", $cost)) {
			$errors = $errors."Invalid ".$event_name." cost.<br />";
		}
	}

PHP:

 

just add in a square bracket at the start [$, etc ]... i think that should fix it