To help me with "czy" and forming the question i translate "czy" as english "so" followed by the statement in a questioning tone.
So, this hat is expensive? = Czy ten kapelusz jest drogi = Is this hat expensive?
I know "so" is not a valid translation but more a trick to help me understand "czy" and then form or translate the question.
Well, if it works for you... but it really seems contradictory, because it makes you sound as if you're almost certain that this hat is indeed expensive, but in the Polish sentence you have no clue about that...