If the car really does have 400,000 under it’s belt when you go to sell it, the utility gained by having FSD during those 400,000kms would be worth the $10k easily. It’s not like you are getting absolutely nothing of value for $10k. NoAP and a Auto lane change over 400,000km of driving would be a god send.
A call option means you buy the opportunity to retain an increase in value for a fixed price.
if I bet you that the price of an apple that is currently $1 goes to $2 next year, you may sell me a contract that says I can buy an apple from you for $1 in a years time no matter what the market price is.
We may agree that this agreement has a price of 50c that I pay right now to you. Therefore if the price of an apple goes to $1.50 I break even and if it goes to $5 I make a load of money ($3.50) as you are forced to sell me an apple that costs $5 for $1 as per our agreement. If for whatever reason the price of the apple goes to 10c, you make extra money ($1.40). It’s a risk that’s proportional to time and expected return hence the price of the contract is highly variable.
For FSD, you are effectively betting that the value of this option increase over time and by purchasing it now, you are effectively fixing your cost and creating an unlimited upside (FSD could go up to any price and you retain all of it) and a fixed downside (can’t cost you more than what you paid for it). The expiry date instead of being a fixed 1yr term like in the apple example is whenever you need to sell your car which is another variable to consider. If you don’t need to sell for many years, the expected return is higher and therefore risk is lower, if it’s only a few years it’s a much higher risk that the value isn’t fully realised yet.