Most pet stores carry tetracycline. THat's about as good as you're gonna get without going to the vet.
Baytril injections or tabs are what you need, they wipe out infections fast. But, it's vet only...
You can get Tylan from most farm supply, but personally, I think Tylan is not good for smaller animals...
From your description, it sounds like RI, but if you keep them in tanks, it could get worse, no matter how clean you keep the cage. They really need good ventilation to remove the ammonia.
Good luck, hope you wipe it out...
Clean the water bottle daily, to help stop spread. Call a vet, maybe they'll work with you, and give you a good discount..