There are companies that collect this information, but it's proprietary
and unless you find a pirated copy somewhere I doubt you'll see fees for
private dentists.
    There are magazines with names like "Dental Economics" that can
generally be found in dental school libraries.  Most of these do fee
surveys every year, but I have my doubts about how representative their
data is.  After all, it is a self-reporting survey.  Generally broken
down by region rather than state.
    Some dental schools may post their fees in the clinics.  I believe
NYUCD did.  Of course this was long before the web was a glimmer.

Steve