Incredible experience
$4 is an amazingly small price to pay for admission to one of the most awe-inspiring places we've ever seen. If you're Catholic, the statues, the scenes portrayed in stained glass, the small side altars and chapels, the baptismal font and confessionals all take on increased significance. Even if you're not Catholic, the interior of the church and its main altar are breathtaking.
And don't forget to stop behind directly behind the main altar to see the smaller chapel. It's another stunning place, with distinctly more modern architecture due to rebuilding after a fire.
My wife has traveled Europe extensively. According to her, this is the most beautiful church she has ever seen.
As for the one goof who griped about a church charging $4 for a tour of the building, maybe YOU ought to get appointed pastor... and then figure out a way to pay for the lights, heat, maintenance and upkeep of the place. $4 is a bargain, especially if it keeps open a place that inspires thousands of visitors to contemplate the divine. Cheapskate.