Half an hour costs 3 zl ($0.75), no limit on time, and there are three times more PC units than there are at the EMPiK so you don't have to queue up.
The exact address is 30, Florianska St. and that's easy to find: look for the Pod Zlota Pipa restaurant sign with Kaiser Franz Josef in it. The internet place is in the gateway to your left.
And while you're there, check the Pod Zlota Pipa pub & restaurant in the courtyard! - see my Restaurant tips for this one :-)

