Emergency Care Needed: Cheddar

This is our boy, Cheddar. We adopted him back in July in when someone we knew had an urgent re-homing situation, where Cheddar and his brother needed a home ASAP. From the start we were unknowingly misled about his age, and he came with a wound on his back leg and the abscess on his left cheek. After weeks of going around from vet to animal hospitals, nobody could figure out what was going on with this abscess. It has burst and come back three times since late July of this year. We took him to the best vet we knew, where they ran hours worth of tests and bloodwork to figure it out. Cheddar has three open wounds on his neck, all infected with an aggressive bacteria that we're waiting on results from. As of now, the doctor we took him to said it could range from FIV to intense cheek cancer. He's currently in a cone praying his infected abscess heals with strong antibiotics and pain medicine, and miserably itchy in pain. We spoke with a doctor and was told Cheddar has necrotic tissue continuously growing in his neck, and if spreading continues the abscess will return and the tissue will eventually eat away at his jaw. He needs an extensive surgery and a CT scan, which costs $5000 alone, to stop the reoccurring abscess in his neck tissue . Please, please help us save our boy.