Since the SkyWest figures include a substantial amount of Brasilias, I'm guessing the CRJ costs are lower than shown for SkyWest, but I don't know how much. Clearly, the bottom line is, if you can fill a plane, fill as big a plane as you can. If not, use the smallest that will carry the load.
That means that for every seat that SWA and Skywest flew for one mile, it cost SWA $00.0754 and and Skywest $00.1890 to provide that seat. If you take out the cost of crew, the 737 would seem to be able to fly one seat for one mile for $00.047 and the smaller aircraft that are flown by Skywest required $00.13 to to provide the same seat. Meaning (very, very roughly) that a 737 only costs a third as much to operate as the E120s and CRJ's. four point seven cents versus thirteen cents.
You may be able to find some raw data on the web sites of bombardier.com (for the CL-65 & CL-700) and embraer.com for the EMB-145.
While not necessarily broken down into CASM, you can derive estimates by taking the direct operating costs and doing the math yourself.
I'm certain you know that CASM for the same aircraft will vary depending on the operating airline. For example while SWA runs at 7.45 for the 73, I believe DAL is 10.46 and AAA is almost 13. I notice in the example above that SKYW was shown at 19.3 (with all the numbers including crew). I assume that averages the jets and the turboprops. For the same equipment, CMR was 14.6.
In every case however, you will find that the CASM of the regional jet is substantially higher than the narrow-body DC-9 and 737. One of the reason why regional jets cannot compe with mainline jets (or take mainline jobs). The numbers aren't there.