Hi Gelksy,
Thank you for contacting us.
At this point we can't specify which option would be the cheapest as this varies depending on the destination itself. May we suggest you to get in touch with our call center agents (
http://bit.ly/1xRL76b) who will be happy to do the necessary calculation to find a suitable flight to upgrade to Platinum status.
Please let us know if you have further questions.
Thanks
*RM