I am surprised how all posters here posted here the answer for HOW CHEAPLY?
more importantly, how costly it would be to visit Poland
That is why. The OP is clearly on a budget and if cost were of no importance, he wouldn't have mentioned it in the first place.
@Randal, it would be easier for people to help you if you give more information. You don't say whereabouts or for how long you will be staying in Poland. To be honest, Poland can be as cheap or expensive as you want to make it, but if you are going to be staying in e/g Warsaw or Kraków, prices will be higher than in the towns/villages.