The vet just now called me and told me that with the IV he's doing better and he's starting to eat. They think they might have an infection, so they're flushing him with antibiotics and he was dehydrated (Which is what I was worried about since he was throwing up so much after drinking).
They want to keep him til Thursday. Which, hopefully, isn't too bad, just two nights, and whatever other fees they throw on me. So will still probably be a $1k+ vet bill, but I'm hoping I can pay for it on my credit card and give me some time to pay it off over time.