I'm afraid you have this…
I'm afraid you have this largely backwards. The Tesla gull wing door design for the model x is complicated, expensive, and unreliable. None of these traits are a good fit for a budget car. They very much do not simplify the car, they add considerable complexity.
The model 3 is already so bare bones that the driver doesn't even get instrument gauges, instead the center screen has to do double duty as all driver gauges and as gauges for the climate control system and radio and everything else. If they had to strip it down that badly and it still couldn't be made cheaply enough, I don't think they're going to add something as expensive as gullwing doors to the cheap one.
That's if the cheap one ever materializes. The cybertruck is being sold well above its announced price point.