Flixbus is your answer to cheap intercity (and even International) travel. Go online, buy your cheap ticket in advance (the sooner, the cheaper) and away you go. The coaches are modern, have air-con, toilets, charger sockets and even wifi. Depending on where you're going, services leave either from the bus stances at Metro Młociny, Metro Wilanowska, in front of the Palace of Culture & Science, from Warsaw Chopin Airport and from Warsaw West Train/Bus Station.

Flixbuses take you around Europe, but locally, too. You can take them straight up to/from Modlin Airport from a variety of Warsaw stations for around 50 zł!