I'm surprised that nobody has noticed that the price was set at 42k because it's another one of Musk's 420 (aka weed) jokes, and not because of any specific data showing that is the optimal price point for this offering.
He will run on the vague impression people had of him being a cool guy who smokes weed for the next 2 decades. I hope he goes to Mars so we don't have to hear about him, or at least we'll have an 8 minute delay?
It's a luxury service. There is no optimal price outside of "high enough to prevent entities for whom money is an object from applying".