I really hope your able to get the funds you need. I forgot to mention this earlier, you may also try calling your local humane society, I think sometimes they're able to do lower-cost care.
I very much understand how this is, my cat, Boo, had an illness that would've been fatal if we hadn't gotten him care in time. Thankfully our vet offered a CreditCare that let us space payments out on the bill. It's been six years now and he's a healty 8 year old.