Travel / Cracow - Gdynia, what is the best way to travel between the two? [11]

The matter is flight from Kiev to Cracow is really cheap, but to Gdansk - it's not (
Direct train to Gdansk is also expensive. And I'd like to see smth of Poland. It must be great )
Thank you for answers. As i see the cheapest way is train. Don't you know, is there any opportunity of international booking?