Feral cat Bunny is very sick

Bunny is an old toothless FIV+ kitty who’s had a hard life. I care for a small colony of feral cats in Baltimore City and Bunny came to my colony about 5 years ago. He has always been a shy, tubby boy. A little over 2 weeks ago I noticed he couldn’t walk straight, was falling over, and had dark brown fluid coming from his ears. He went to metroferals where he received a thorough ear cleaning, antibiotics, and steroids, but the infection has persisted. His follow up appointment at academy vet in Baltimore showed branch chain cocci bacteria and both inner and outer ear infections, including an abscess. Poor toothless Bunny is going to require more recovery and care than expected. I’ve turned my spare bathroom into a studio apartment for him, so he can rest safely. He’s continuing with antibiotics, as well as meclizine to help with his falling. He’ll require follow up vet visits to ensure he is healing. Any help with Bunny would be appreciated. So far his vet costs have been over $400 and are expected to reach $1000 if not more. Bunny is a sweet boy who deserves a chance to recover. Please help and share if you can. Thank you