How to add currency strings (non-standardized input) together in PHP?

$string1 = "$50,000";
$string2 = "$50000";
$string3 = "50,000";
$total = (double)$string1 + (double)$string2 + (double)$string3;
echo $total;

function validateCurrency($string)
{
    return preg_match('/^$?(d{1,3})(,d{3})*(.d{2})?$/', $string) ||
           preg_match('/^$?d+(.d{2})?$/', $string);
}

function makeCurrency($string)
{
    $newstring = "";

    $array = str_split($string);
    foreach($array as $char)
    {
        if (($char >= '0' && $char <= '9') || $char == '.')
        {
            $newstring .= $char;
        }
    }

    return $newstring;
}

$x = 1.0;
for ($ii=0; $ii < 10; $ii++) {
  $x = $x - .1;
}
var_dump($x);

m/^$?(d+)(?:.(dd))?$/
 $value = $1 + $2/100;

(pseudocode)
newnumber = replace(oldnumber, /[^0-9.]/, //)

double(newnumber)