EVs are simpler devices than gasoline-powered vehicles. They have a smaller number of parts, making them easier to assemble. At similar scale to gas vehicles, electric vehicles should indeed be lower cost to built.
In addition, EVs have many fewer moving parts (in the engine and drivetrain in particular) than internal combustion vehicles. That further means lower construction cost for the most complex and costly part of a vehicle, and far lower maintenance cost.
While it is true, the engine and drive train has fewer parts, when I reduce it to motor and battery. But in fact every EV has a gear, including the Tesla. Yes, this gear is much simpler, but it is there and even runs with oil that has to be replaced every 100.000 miles like in every other car. The battery is as complex as an engine itself. Because you need to measure lots of sensors values and to control that it will not explode and not wear down to fast. Every battery, including the one in the Tesla, has a dedicated heating and cooling system just for the battery within the battery.
Then also lots of parts in car are the very same like brakes, steering, air condition, windows, and so. Remember that a current car is about 30% software and will be more in future. But there is only 1 engine control unit. The most of the parts are other things to control safety or personal comfort.
Electric vehicles, today, have lower total costs per mile than equivalent gasoline-powered vehicles, due to lower energy costs of electricity and the lower maintenance costs.
That neglects the fact, that most of the maintenance costs are not engine related. Like the brakes have to be regularly checked. It neglects the fact, that a battery will wear out sometimes between 3 to 6 years and has to be replaced, which is a huge cost related issue. The guarantee Tesla has, does not help, because you will pay for that guarantee otherwise.