I was surprised by your claim so I checked... the Tesla website currently allows me to configure a Model 3 that is $39,500 before discounts for estimated delivery in two weeks. Not $35k but far less than $48k too.
Or if you prefer you can order the $39.5k one and call up service and get them to change the settings, and then they'll send you a refund of $4,500.
Does this all sound strange? Sure, but I guess they have their reasons for doing it, which seem to be mainly to keep the menu simple and steer people toward the best value, because the $39.5k car is a better value than the $35k car.
So the extra $4.5k is pure margin.