I have an as-new Celestron Radial Guider model #94176 that is surplus to requirements. I got it with a used C8 that I have never used for deep-sky imaging, and don't expect to!
This is designed to fit on the visual back of a C6, C8, C9.25, C11 or C14 and was intended for use for manual guiding (yikes!) with a guiding eyepiece. I have seen some posts on CloudNights that show it being used with a guide camera, so I expect it will work - although I haven't tried it myself. The "camera-side" has a T2 male thread, to which you could attach the usual adapter to fit to a DSLR/mirrorless or astro-camera - you might need some spacers to get the correct back-focus distance though.
You also combine this with a focal reducer (I'll post an ad for one of these soon).
Let me know if interested and if you'd like me to test any particular configurations. The only camera I can test with is a Zwo ASI120MC with the 1.25" eyepiece adapter.
Looking for about $75 + postage.
