I recall doing some homework before I put a deposit down to find which documents I should try to get the dealer to sign to lock in a price. My takeaway was there's no standard, formal option
you just have to hope you get a good guy dealer?
Anyhow I just re-researched a bit how I came to that conclusion. The first legally binding document that would come into play normally is a buyers order sheet. This is usually worked up very close to sale if not day-of. It basically wouldn't be possible (or wise for buyer) to do more than a few weeks out from sale, aside from locking in a good price on the car itself. It locks in every other variable in the sale too.
Short of drafting up some sort of weird contract yourself (which I would balk at if I was a dealer) I don't think there are any common legally binding options for a buyer until much later. I welcome any specific examples otherwise. And I really wish I posted this in the waitlist thread!!! I'm going to at least link to here in that thread.