Allusion, the Supreme Court has found taxation on the exercise of other rights [caselaw.lp.findlaw.com] to be unconstitutional. However, the contours of the 2nd Amendment are still being hashed out in the courts, so it'll be awhile before we can challenge schemes like those proposed in Illinois.
Tom - Thank you for the informative read. It sounds like if something like the proposed registration fee should pass, it will be a legal battle all the way to the SCOTUS.
"With great power, there must also come great responsibility." - Stan Lee
"All that is necessary for evil to triumph is for good men to do nothing." - Edmund Burke