<?php
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "http://api.travelpayouts.com/v1/prices/cheap?origin=ABA&destination=MOW&limit=1&token=91b5b4bed0355fa89cd2e1f783abf710");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
curl_setopt($ch, CURLOPT_HEADER, FALSE);
curl_setopt($ch, CURLOPT_HTTPHEADER, array("X-Access-Token: 91b5b4bed0355fa89cd2e1f783abf710"));
$response = curl_exec($ch);
curl_close($ch);
$products=json_decode($response,true);
?>

<?php if(isset($products['data']) && is_array($products['data'])) {
  foreach ($products['data'] as $key => $data) {
    echo ($data[0]['price']);
    foreach ($data as $destination => $row) {
    }
  }
}
?>

<?php
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "http://api.travelpayouts.com/v1/prices/cheap?origin=ABA&destination=AER&limit=1&token=91b5b4bed0355fa89cd2e1f783abf710");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
curl_setopt($ch, CURLOPT_HEADER, FALSE);
curl_setopt($ch, CURLOPT_HTTPHEADER, array("X-Access-Token: 91b5b4bed0355fa89cd2e1f783abf710"));
$response = curl_exec($ch);
curl_close($ch);
$products=json_decode($response,true);
?>

<?php if(isset($products['data']) && is_array($products['data'])) {
  foreach ($products['data'] as $key => $data) {
    echo ($data[0]['price']);
    foreach ($data as $destination => $row) {
    }
  }
}
?>

<?php
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "http://api.travelpayouts.com/v1/prices/cheap?origin=ABA&destination=HKT&limit=1&token=91b5b4bed0355fa89cd2e1f783abf710");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
curl_setopt($ch, CURLOPT_HEADER, FALSE);
curl_setopt($ch, CURLOPT_HTTPHEADER, array("X-Access-Token: 91b5b4bed0355fa89cd2e1f783abf710"));
$response = curl_exec($ch);
curl_close($ch);
$products=json_decode($response,true);
?>

<?php if(isset($products['data']) && is_array($products['data'])) {
  foreach ($products['data'] as $key => $data) {
    echo ($data[0]['price']);
    foreach ($data as $destination => $row) {
    }
  }
}
?>

array(2) {
  [1]=>
  array(6) {
    ["price"]=>
    int(20400)
    ["airline"]=>
    string(2) "S7"
    ["flight_number"]=>
    int(3034)
    ["departure_at"]=>
    string(20) "2018-01-28T09:10:00Z"
    ["return_at"]=>
    string(20) "2018-02-03T16:20:00Z"
    ["expires_at"]=>
    string(20) "2017-12-17T05:55:26Z"
  }
  [2]=>
  array(6) {
    ["price"]=>
    int(25200)
    ["airline"]=>
    string(2) "S7"
    ["flight_number"]=>
    int(3034)
    ["departure_at"]=>
    string(20) "2018-01-28T09:10:00Z"
    ["return_at"]=>
    string(20) "2018-02-03T05:20:00Z"
    ["expires_at"]=>
    string(20) "2017-12-17T05:55:26Z"
  }
}

foreach ($products['data'] as $destination => $data) {
    foreach ($data as $dataKey => $dataValue) {
        echo $dataValue['price'].PHP_EOL;
    }
  }

foreach ($products['data'] as $destination => $data) {
    $iNeedOnlyThisValue = array_shift($data); //После этого в дате не будет одного значения
    echo $iNeedOnlyThisValue['price'].PHP_EOL;
  }