They weren't the cheapest, but I used CIBTvisas, which is the company recommended by
ABD (at least they were in 2017, I have no idea about now
). They were very easy to work with, and really knew their stuff, and once they accepted all my documentation, the next I heard was that I got my Visa. It's kind of frustrating, because there's a window of like 3 months where you can apply, and leaving it to that late was really nerve-wracking for me. But they do that because you don't know how long of a Visa China will decide to give you, and you don't want to get one that will expire before the trip is over. (They can be anything from 6 months to 10 years).