$inventory = array(

   array("type"=>"fruit", "price"=>3.50),
   array("type"=>"milk", "price"=>2.90),
   array("type"=>"pork", "price"=>5.43),

);
$price = array();
foreach ($inventory as $key => $row)
{
    $price[$key] = $row['price'];
}
echo 'Before Sort';
echo '<pre>';print_r($inventory);echo '</pre>';
echo 'Price array()';
echo '<pre>';print_r($price);echo '</pre>';
array_multisort($price, SORT_DESC, $inventory);
echo '<pre>';print_r($inventory);echo '</pre>';


// result

Before Sort

Array
(
    [0] => Array
        (
            [type] => fruit
            [price] => 3.5
        )

    [1] => Array
        (
            [type] => milk
            [price] => 2.9
        )

    [2] => Array
        (
            [type] => pork
            [price] => 5.43
        )

)

Price array()

Array
(
    [0] => 3.5
    [1] => 2.9
    [2] => 5.43
)

Array
(
    [0] => Array
        (
            [type] => pork
            [price] => 5.43
        )

    [1] => Array
        (
            [type] => fruit
            [price] => 3.5
        )

    [2] => Array
        (
            [type] => milk
            [price] => 2.9
        )

)