I think what you want to do, is to concatenate all of the JSON responses and put them together, instead of creating 3 different array elements in results[]; Look into array_merge():
$result = array();
$arr1 = json_decode("json api response url", true);
$arr2 = json_decode("json api response url 2", true);
$arr3 = json_decode("json api response url 3", true);
$result = array_merge($arr1['Info'], $arr2['Info'], $arr3['Info']);
$decoded = $result;
usort($decoded, function($a, $b) { return $a['price'] > $b['price'] ? 1 : -1; });
foreach($decoded as $row) {
echo $row['price'];
}