Care credit or scratch pay
If it's a feline leukemia and they are passing rapidly it's very likely that they wont be able to be saved. Not knowing the situation I'm just making a guess drawing on my experience with other people and this is a pretty common problem especially with feral cats. Unfortunately the pet emergency clinic will require that you provide payment in full. They may not treat them at all if it's a infectious disease but I cant speak for them. Call them and get their advice on how you can proceed but be prepared for the worst. I'm sorry to say that but vet care is a real big expense especially on an emergency basis.
Call a local rescue group to see if they can assist.
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