Sorry, this got kind of confusing, lol! So if a school uses CSDCAS, the GRE code you need to use to send them your score will be different than that school's 'regular' GRE code - so every school that uses CSDCAS (or at least every school I applied to that used it, which was 4) has a special CSDCAS GRE code (so for example, JMU's regular GRE code is 5392, but their CSDCAS code, and the one you would have to use if you were applying to their program, is 1043). I didn't know that there were separate CSDCAS codes when I took the GRE, so when I chose the schools I wanted to send my scores to (for free) I just chose the regular GRE codes (not the CSDCAS ones) and unfortunately, 3 out of the 4 scores I sent were to CSDCAS schools. I later found out that there were different CSDCAS codes, and had to send my scores to those schools again, which is why I 'wasted' 3 of my schools. I don't really remember much about searching for schools when choosing which ones I wanted to send scores to (maybe someone else here does) but I imagine that you can send the scores to the correct CSDCAS codes for free before (or was it after?) the test. You can find the CSDCAS codes on most program's admission websites, and also on the CSDCAS website (if you have an account, I guess). So basically, as long as you send your scores to the right codes, it doesn't matter if the school is CSDCAS or not - it will cost the same and you won't be wasting any money).
As for the cost of applying to CSDCAS schools, it is more expensive. The $100 mentioned above is for the first CSDCAS school you apply to. For every subsequent school, it's $45. But most CSDCAS schools also have supplemental applications, which comes with a separate fee also (although one of the four CSDCAS schools I applied to did not have a supplemental app) so that's where the extra expense comes in. That being said, there are a few perks to CSDCAS. It is much easier for recommenders (as far as I know) because they only have to send one letter to CSDCAS, no matter how many schools you applied to through it (so I applied to 7 total schools, 4 CSDCAS and 3 non-CSDCAS, and my recommenders only had to submit to 4 places, not 7). Similarly, you only have to submit your transcript to CSDCAS once, which can be helpful if you have taken classes in a lot of places, or if your school charges a fee to send transcripts. I did not run into any of the CSDCAS problems that a lot of people did (lost transcripts, etc.) so I can't attest much to that - but do make sure you are mindful of the fact that it does take a while for CSDCAS to verify your application, especially the later you complete it, and some schools have verified deadlines (not just completed) - but CSDCAS tells you all this, and it's nothing for you to get too concerned about now!
I hope this is helpful and clears up some confusion - let me know if it's still confusing! Good luck!!