By keeping the sick ones separated from the ones that are still healthy, the chances of all of your turtles becoming infected are greatly diminished. Its called quarantine, and is an effective way of preventing contagion from spreading. I just treated one of mine for the same thing: isolated him to keep him away from the others, took him to the vet promptly, paid the vet willingly, and put him back in the general population when he'd recovered. All of our turtles live outside year round, and once in while, one of them comes down with something. We have not lost one yet, nor do we intend to.
I am not condescending, but rather trying to point out to you the error of your ways, so to speak.
Within the last couple of days, on this forum, you stated that you had offered to purchase 10 eastern box turtles for $200 from a less-than-scrupulous dealer, ostensibly to "rescue" them from ending up in pet stores or in the hands of someone who might mistreat/neglect them. Seeing the irony yet?
Luckily for you (and the turtles) that you did not buy ten more box turtles that you can't afford to treat should they get sick.
You have an opportunity to learn from this experience and to become a better turtle keeper as a result: you'd do well to lose the attitude.
Haven't you ever heard of having an emergency fund? How about a plain old savings account? If you are not financially able to provide basic care for your pets, or any other dependants, then you should take a long hard look at yourself and grow up.
By the way, I have 4 dogs, and 4 cats, in addition to box turtles, and I am fully prepared to spend whatever is necessary and/or appropriate for their care, simply because I am not a hypocrite when I say I'm an animal lover.
Regards
Stephanie