I don't see the false dilemma, I think you're hinting at a third choice where the ambulance company charges a price that is not extortionate, but if that was part of the hypothetical then, sure, I would have chosen to get my emergency care from the company that charges less (but it's not, the GP postulated that all ambulance companies charge 80%).

Either way it's not exploitation, even if there's a company that charges prices that always bankrupt their patients, I still choose broke over dead, and if I wanted to choose dead I can do that too.