Try Carecredit.com:
CareCredit - As a service to our clients, we are pleased to offer CareCredit, the nation’s leading patient client plan. With CareCredit you can finance 100% of your vet care and there are no upfront costs, no annual fees, and no pre-payment penalties. So, you can begin treatment today and conveniently pay with low, monthly payments.
CareCredit offers several payment plans so you can find one that works best for you. With the popular No Interest Payment Plans* there are no interest charges if you pay your balance in full within the specified time period. Monthly payments can be as low as 3% of your balance. For treatment plans from $1,500 to $25,000, CareCredit offers 24, 36, and 48 month plan options with low monthly payments available.
Also check out: angels4animals .org
many local humane societies have funds available for emergency veterinary care as grants or loans for low-income pet owners.
google "financial assistance vet care" and there are lots of possibilities