That's the thing about volume that many seem to miss. The unit cost of production goes down when you increase volume. This means that overall profit margins increase. It's the primary motivating force behind the standardization of almost all manufacturing methods. From cars to tv's to medications. Highest volume possible for the lowest amount of minimally skilled people you can squeak by with. It's the Henry Ford model and it built industrialized America, then abandoned it for China and India because human costs are lower and environmental protections are almost nonexistent. New factories are not needed for step production increases and saline can produced on demand on site with minimal equipment. With nothing more than a high school chemistry set, oven, glass IV bottle, basic surgical tubing and needles you could create sterilized IV saline solutions in a home. I wouldn't recommend it though.
You also are missing the point of collective bargaining and its impact on market forces. Today, some large hospital networks have the bargaining power in the provider/insurance market. This means that they have the ability to demand higher payments which ultimately come from the patients. No difference in service compared to their smaller cousins, just better bargaining position. In a single payer system, the insurer has the power in that bargaining process which means that hospitals can bill any amount they want to the insurance company, they just won't get it. In a single payer system, there are no uninsured so there is no way to over bill patients and there are no uncovered losses to make up either. As a whole, this places market pressure on the providers to become more efficient in delivering healthcare services. You can charge $20 to hook up an IV or $2 million but you'll receive whatever payment the single insurance company is willing to pay and every one of your patients is covered by that insurance company. Now it's on you as the service provider to figure out exactly what your unit service costs are determine the best way to provide that service within an acceptable profit margin. That in turn places market pressure on pharmaceutical companies to keep manufacturing costs in check.
It's worth noting that during this supposed evaluation of how to provide saline in 2015, Baxter's financial performance was so good that it had a stock split. It's fun for corporations in America to cry poor me to the press when they're posting record breaking profits. It's all a theater to mask full on corporate greed. That FDA labelling of saline as a national shortage was, I'm relatively sure, paid for in lobbying funds. It's just a polite way to say bribes to federal officials.
Thank you,
CriticalThinker