There is not a ton of money to be made by having this as an extra charge in my opinion. If you assume the park will have attendance around 3 million and with the ride opening later in the year maybe 2.5 million people will have the chance to go through. To be even more conservative I'll say it will not be open for haunt and then maybe there are 2 million possible visitors. If they can get ten percent of park visitors to enter, and that may be high considering there are a lot of potential pass holders/repeat viewers, that is only $1,000,000 plus whatever they make in souvenirs. I would think the cost of this project would be close to that, if not more, with all the costs considered.
In my opinion though, and I have no evidence to back this up, maybe an extra charge was the only way to add this. If they didn't have the money in the budget maybe charging is the only way to add anything extra to the park this year. So in essence this is paying for itself and it is a choice between adding this with an upcharge or adding nothing at all. That is why I am happy it's coming.