I shipped it UPS
That's surely the most expensive way (maybe besides Fedex) to ship stuff to Poland. If you live in NY, or Chicago area, the cheapest place is Polamer.com or Domashipping.com. I think one out of 1000 Poles living in the US would use UPS to send stuff to Poland.
And another (best) way would be to either personally take the laptop while flying to Poland or ask someone you know to ship it for you.