You have gotten good comments here. I would like to add mine to the list. If he scored poorly on the Nov SAT he must do something other than take endless practice tests to improve his score. One of the things he can do that costs very little money is to analyze the questions he gets wrong and see if there is a pattern to them. Have him work to improve his performance on the types of questions he is getting wrong.
Since you say you are a full pay family I will also suggest a private SAT tutor. The reason so many people complain about kids who prep for standardized tests is that it works. You might not have enough time for it to make a difference in December but if he retakes in the spring or fall you should consider it.
I would also try the ACT. I have three kids and they all preferred it to the SAT. We are also full pay and our oldest got good merit based aid at CWRU but it did not bring the cost down to the same as our state flagship. He did graduate from CWRU and had a good experience there.