Also, in contract law, 'unusual' and 'unreasonable' have a very large overlap in their venn diagram.
If the seller and buyer are related, tax obligations are different because it involves a gift or implied compensation, but that's not what we're talking about here.
So it is indeed possible to pay no more than $1 for a car. As for registering the title in your name, that's a different story, and has nothing to do with the actual sale.