Holly needs a limb amputated

Hi this is my dog Holly. She is a 12 year old Chihuahua that has soft tissue sarcoma. I had her tumor removed twice already and the vet said it was just going to keep coming back. The vet has now said that removing the tumor is not an option anymore and it is time for amputation. Her tumor is coming back with vengeance and keeps growing faster and faster by the day. My vet also said Holly cannot get cleared for surgery until she goes to a canine cardiologist which is yet another hefty bill. I have been trying to get my vet to give me an exact dollar amount because I am trying to figure this all out and she finally came back to me and said its going to be anywhere between $5,000-$8,500 and unfortunately, I do not have that money laying around at the moment for an emergency like this. Smaller chihuahuas can possibly live up to 16-20 years so she might have some good years left in her. I've had her since she was 2 months old and she means the world to me. I was honestly going to put her down because I don't have the funds for amputation but I am not ready to say goodbye to her so hopefully I can raise enough money so she can live a bit longer.