As you can see, that Resulthas more than one subarray, if you need details related to the first record, you can use your index0
$price = $hotel['Result'][0]['Room']['SellingPrice']['Currency'] . ' ' . $hotel['Result'][0]['Room']['SellingPrice']['Amount'] ;
You can change the index [0]with any array of results that you need, otherwise you can loop through the t20> subcategories and get all the necessary information about them
foreach($array_data['HotelAvailability'] as $hotel)
{
$id = $hotel['Hotel']['Id'];
$name = $hotel['Hotel']['Name'];
$region = $hotel['Hotel']['Region']['Name'];
$stars = $hotel['Hotel']['Stars'];
foreach($hotel['Result'] as $result)
{
echo $result['Room']['SellingPrice']['Currency'] . ' ' . $result['Room']['SellingPrice']['Amount'];
}
}