Verifying an amount

[Enlightened]

Hello, I posted earlier about using regex to verify an amount inputted. They suggested using number_format();
Should this do the job or am i looking for something different all together.

	$number = $_POST['amount'];
	$amount = number_format($number, 2, '.', '');
	if(isset($_POST['amount']) && $amount < 25.00 || strlen($_POST['amount']) < 4 || strlen($_POST['amount']) > 9
	{
		$errors[] = "The minimum payment amount is $25.00 and must be in proper format.";
		}else{
		$amt = trim($amount);
	}