Well, if you have to get an ID to vote and have to pay a fee to get an ID, wouldn't that be a poll tax?
Yup. In fact Wisconsin's new photo ID to vote law was judged in March to be unconstitutional despite containing provisions for free IDs. The free ID provisions were an attempt to make the law pass constitutional muster, but were apparently not sufficient.
This is good news.
That was the ruling of the trial judge, ruling under the Wisconsin rather than the US Constitution. The Wisconsin Supreme Court refused to hear it on an expedited basis, so it will wend its way through a state appellate court, and eventually probably end up with the Wisconsin Supreme Court (which tends to be Pub friendly - the judges are elected).