Keeping my rescue dog alive

Hi I adopted my dog from the pound in 2013 he had been abused . He is bringing amazing joy to my children. He is my best friend. 18months ago he was diagnosed with diabetes, his insulin he needs is $120 a week to keep him alive. When I separated 4 years ago Bobby was my rock and children's rock. My youngest suffers from cerebral palsy he needs Bobby who keeps him smiling and happy. The vet bills are around $800 a month. I can't afford them anymore 😪 but I can't put Bobby down. I'm a single mum on one income struggling and have used my hardship kiwisaver have gone into massive debt . Please can someone help me keep our best friend alive .