[wholesalePrices] => Array
    (
        [0] => Array
            (
                [quantity] => 10
                [price] => 9.99
            )

        [1] => Array
            (
                [quantity] => 25
                [price] => 8
            )

        [2] => Array
            (
                [quantity] => 50
                [price] => 6
            )

        [3] => Array
            (
                [quantity] => 100
                [price] => 4
            )

<form>
   <input type="text" name="quantity" placeholder="Quantity" />
   <input type="text" name="price" placeholder="Costing" readonly />
   <input type="submit" name="submit" value="Show Cost" />
</form>

$data['wholesalePrices'] =
     array(
            'quantity' => 10, 'price' => 9.99,
            'quantity' => 25, 'price' => 8,
            'quantity' => 50, 'price' => 6,
            'quantity' => 100, 'price' => 4
     );
$qty = $_POST['quantity'];

if(in_array($qty , $data['wholesalePrices'])) {
    echo "price exist";
} else {
    echo "Not Matched";
}