Its vet time and time to keep the sick animal away from your others and deal with them last after you have changed water and spot cleaned your healthy snakes first as to not spread the problem.

As for vet prices, it depends on the vet. When I had to take my beardie in for slight RI, the bill was around $270. What you are probably looking at is the office visit, a culture, a wide spectrum antibiotic to start with until the culture comes back, then possibly switching antibiotics depending if the germ is sensitive to the first antibiotic.

As for keeping in the same room, I kept my beardie in the snakes room even when she had slight RI. I did deal with her last though and always scrubbed my hands down with F10 and soap between all animals. Never use the same utensils or anything between a sick animal and the rest of your collection. I'm kind of OCD though and I always wipe down tables and everything with F10.