//get all information about an item (a single HTTP request is made), save them in a variable (jsonObject),
//make necessary adjustment on item's value and return the result
function GetItem(itemID) {
  var myUrl = "http://www.gw2spidy.com/api/v0.9/json/item/" + escape(itemID);
  var jsonData = UrlFetchApp.fetch(myUrl);
  var jsonString = jsonData.getContentText();
  var jsonObject = JSON.parse(jsonString).result;
  jsonObject.min_sale_unit_price=jsonObject.min_sale_unit_price / 100;
  jsonObject.sale_price_change_last_hour=jsonObject.sale_price_change_last_hour / 100;
  jsonObject.max_offer_unit_price=jsonObject.max_offer_unit_price / 100;
  jsonObject.offer_price_change_last_hour= jsonObject.offer_price_change_last_hour / 100;
  return jsonObject;
}

// functions call example for prices of Glob of Ectoplasm:
var ecto = GetItem(19721);

//get adjusted values getting property of the item
var sell=ecto.min_sale_unit_price;
var sell_changed=ecto.sale_price_change_last_hour;
var buy=ecto.max_offer_unit_price;
var buy_changed=ecto.offer_price_change_last_hour;