Getting a coin to grade at the top of the known grade standard for Franklins (PF 69) is not. Combine THAT with toning and the multiplier is insane.
Your coin, while nice, is not going to be the top tier of Mint State coins with regard to condition and therefore the toning multiplier is mitigated.
Also not all coin dealers are the geniuses that Dr. Rodebaugh is.
I reiterate that I would take the $500 and be quite pleased
I will be very surprised, happily for you, if you are able to get more than that, especially after figuring in costs and time.
Let us know how it works out for you!