Well, if you want to move in Poland, this is the best advice you can ever get. One of the world best bus companies is polish: PolskiBus
Their prices are among the cheapest in the continent, and the first bus ticket is just 1 zl (0.25 cent) in any line, so if you are among the first you will do about 600 km for few euros.
Also, the buses are very good, comfortable and with plenty of room for legs and suitcase, as well as individual plugs and Wifi. If you are lucky you can be in the front window of the second floor and enjoy the amazing scenery of Poland.
The easiest way to book is throught the website, is fast and safe, and you only need the reservation code in phone or in a paper.
So if you plan to travel to Poland, remember that transport will be very cheap!
Here you will short posts with very interesting information that can make you save a lot of money when traveling