My first rule of thumb is that all chinese silver dollars are fake.
It sounds like you think that's not the case here.
I'm certain that if it is genuine the slab will more than make up for the costs. It might turn it from a coin worth tens of dollars to hundreds of dollars.
Slabbing isn't just an opinion on grade, it is a very valuable opinion on authenticity.
My biggest concern would be that it is not genuine, and then the $75 fee will truly have been wasted.
I'd take good pics, weight, measurements, etc., and post them on a more widely visited coin collecting website. I am partial to coincommunity world coin section, but there is also cointalk, collectorsuniverse (PCGS own forum), and NGC forums.
Sometimes there are simple clues to fakes like the font or the symbols aren't correct, but some clues are more subtle. At the bigger sites there are often more experienced collectors that can point those things out.
Then depending on how you feel about that free screening process you may decide to submit it.
Good luck,
-wheatiefan