FWIW, we purchased a black (June) 2018 M3 with 44k miles, FSD, and grandfathered free/included connectivity for $40k about 2 weeks ago. We bought the car in Seattle but are AZ residents, which means no state sales tax on private party sales. As an added bonus, AZ still charges next to nothing for EV registration, which in our case was about $65 for two years. The bottom line is that with FSD, free connectivity, no tax, and nominal registration cost, I think we did pretty well. And it's a great car--glad we finally took the plunge.
We are driving back to AZ next week--first road trip in the M3. Looking forward to the experience.