def _item_price_with_capacity(which_category, capacity)
      _item_prices_in_category(which_category).find { |item_price| item_price['item']['capacity'].to_i == capacity}
    end
def _item_price_with_capacity(which_category, capacity)
      _item_prices_in_category(which_category).find { |item_price| item_price['item']['capacity'].to_i == capacity}
    end
Searches through the upgrade items prices known to this server for the one that is in a particular category
 and whose capacity matches the value given. Returns the item_price or nil