It's a tough situation to be in and if you're in this situation, I sympathise with you . However there are a few options which may be able to help you out.
Veterinary clinics will understand when the budgets is tight, clinics themselves run on tight budgets. Letting your veterinarian know in advance is the best way to go about it. Veterinarians have many different treatment options available and vets are trained at fitting the treatment options in your available budget. Don’t be afraid to ask for an estimate of expected costs and understand where each cost is coming from.
Clinics work with pet finance companies to offer finance options to our clients. They can help with the application process to see if you are able to get funding through this option. If so the finance company pay the clinic directly and you set up an automatic payment to the finance company staggering the payment over a few weeks. In New Zealand, Petfunders and Vetfinance would be the two most commonly offered and you can try both companies.
Some clinics will offer Afterpay or Oxipay, which is a new payment method that splits your payment up over a fortnightly period to allow you to pay back the cost over the course of a few weeks. Again Afterpay or Oxipay will pay the clinic directly so they can get started on your pet care as soon as you have approval.
Other options would be using credit cards, asking family members for help or crowd funding.
If you think your pet needs urgent help please talk to a veterinarian to discuss your situation and see if they have a way to help you.
As a pet owner you have an obligation to prevent suffering in your pet. Veterinarians will be able to advise on the urgency of the problem and alternative options available to you.
If your tough financial situation has changed to the point where you cannot look after your pet any more there are many charities such as the SPCA, who help with re-homing pets in these sorts of situations so it is always worth reaching out and seeing if they can help you.