I would call around your local dentist and ask if they have a payment plan or know or any other dentist that are low cost. Most dentist are willing to work with patients on cost or payments to help.
Contact your community health center. Also, you could contact local dentists as a lot of them offer discount to seniors. They may even suggest a payment plan where you could pay monthly.
As always, the internet is your best bet. If you go online and simply search for dentists who treat low income seniors, many pages will come up of doctors that fit that billing.