Also they overcharge insurance carriers because they know they'll get less than what they charge so they'll overcharge to get what they really want.
Be aware that insurance companies are now preventing providers from offering lower costs to non-insured. I saw a sign in my dentist office where they said they can no longer offer discounts for non-insured because the insurance companies "are watching". (Can't remember the exact wording). So be sure to ask what the provider will charge.
I, too, used an older CT scan for my CI evaluation. It was about 2-1/2 years since I had it taken but the CI surgeon said it was fine after he looked at it, so I saved myself by not having to get that done.