Tesla currently has 2018 M3 LR models starting in the upper $30s with FSD.
One with 31k miles, FSD, clean history, etc. has an asking price of $42k:
2018 Model 3 | Tesla
I'd suggest pricing yours around $39,900 to start. Yes, FSD is now $10k but not everyone cares about FSD.
I would also suggest getting an offer from CarMax, Carvana and Tesla so you can at least get a sense of a bottom value number. If the high offer comes in at around $35k then a fair private party selling price may be between $35k and $40k. Also, don't forget to factor in any sales tax benefits you may get (depending on state) if you are looking to trade and not just sell the car.