Get most efficient amount of product by volume and price

priceVolume.php

<?php

function vol_price ($needed) {

	$table = array(
		array(250,  0.90),
		array(330,  1.30),
		array(500,  2.20),
		array(1000, 2.50),
		array(1500, 3.00),
		array(2000, 4.50)
	);

	usort($table, function ($a, $b) {
		return ($a[1] / $a[0]) > ($b[1] / $b[0]);
	});

	$left = $needed;

	$res = array();

	foreach ($table as $row)
	{
		list($vol, $price) = $row;

		while ($vol <= $left)
		{
			$res[] = $row;
			$left -= $vol;
		}
	}

	usort($table, function ($a, $b) {
		return $a[0] > $b[0];
	});

	foreach ($table as $ratio => $row)
	{
		list($vol, $price) = $row;

		if ($vol > $left)
		{
			$res[] = $row;
			break;
		}
	}

	return $res;
}

print_r(vol_price(3300));