"If we paid Tesla 2x as much per car, could they really not produce more cars?"
They also fail to privileging the status quo - "If we paid Tesla half as much money, would they produce fewer cars?"
Obviously, they would. Money influences how easily they can produce cars. At the margin there must be decisions related to turning money into efficiency every day. And the same thing must apply for vaccines. The best vaccine expert in the world asked for a yearly sabbatical - 200k wasn't enough to keep them. Double that to 400k? Oh actually it can wait til next year.
The question for people who deny money's ability to produce more vaccines is: why do you admit that any lower price for a vaccine would reduce supply - but you deny that any higher price would increase supply. What magic is this?