My cat has bad dental problems, I don't know what to do..?

Yesterday, two of my cats teeth fell out, I took him to the vet and it turns out a lot more of his teeth are missing--she said that he seems to have a dental disease causing this that some cats get. The total cost for me to have his surgery ie..clean mouth remove teeth etc..is going to be $800 I cannot afford this right now due to a recent financial situation and none of my family members can help me out. I also am worried about the prognosis and the cost of any ongoing care. Should I put him to sleep. I love him with all my heart, but I don't want him to be in pain and it's not fair to him if he can't get proper treatment. This really sucks :(
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One of my cats was thought to have this disease. Vets are not very understanding and most will not let you make payments. Mine won't and I have been going to him for many years. I was told to contact the humane society. They have a system where I am (in Indiana), that is like medicaid, except for your pet. It turned out that my cat did not have the disease, so I never had to ask for the help. I do know that I was told that the disease, is like a cat is allergic to its own teeth, or the plaque on the teeth. They recomended cleaning his teeth and putting him on drugs for the rest of his life. I would definitely ask for help now and not wait. Treatment needs to be started right away.
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