A simple PHP script for testing what cost you should use with your server for password_hash() in PHP 5.5.0+

password_api_test.php

<?php
/**
 * This code will benchmark your server to determine how high of a cost you can
 * afford. You want to set the highest cost that you can without slowing down
 * you server too much. 8-10 is a good baseline, and more is good if your servers
 * are fast enough. The code below aims for ≤ 50 milliseconds stretching time,
 * which is a good baseline for systems handling interactive logins.
 */
function_exists('password_hash') or die("Please use PHP 5.5.0 or higher.");

$timeTarget = 0.5; // 50 milliseconds 

$cost = 8;
do {
    $cost++;
    $start = microtime(true);
    //    as of PHP 5.4, you may use literal notation for arrays
    //password_hash("test", PASSWORD_BCRYPT, ["cost" => $cost]);
    password_hash("test", PASSWORD_BCRYPT, array("cost" => $cost));
    $end = microtime(true);
} while (($end - $start) < $timeTarget);

echo "Appropriate Cost Found: " . $cost . "\n";

// EOF