You are probably right that they won't maintain the old price, but to be fair the website says "Order" at every step of the process.
You click "Order now" from the Model S page, then at the bottom of the configurator it says "Order your Model S", then the fee of $350 is called "Fully refundable order fee".
To be honest, I just want them to start bringing the cars into Australia. My car will be 7 years old in Oct 2023 and I have to sell it before then. I can't think of what else I would buy if the new Model S is still unavailable here.