Please help Tim our 5 month old kitten

Hi everyone, Tim, our youngest sons 5 month old kitten, on Wednesday evening wouldn’t answer our calls to come back in for the night, we reluctantly gave up at 12:30am. Our eldest son popped out to check around 1:30am and found him asleep in the garden even though we left a window open for him. He brought Tim in, who didn’t seem right, but he went straight to sleep. On Thursday morning Tim was led in the hallway, he didn’t attempt to move and grumbled when I picked him up. My wife took him to the vet and it’s the vets opinion (not cast iron fact) that she thinks Tim was attacked. He has a bruised tail, she thinks he’s been kicked in the back legs, his pelvis is broken in 3 places and his front claws are very worn down, all signs he may have been restrained and tried to get away. He’s been at the vets since and we’ve just been told that the operation Tim needs will cost £5000 plus ongoing treatment costs. Unfortunately he’s not insured yet as he’s only just started going out.
My youngest son is 17 and has been struggling with ongoing mental health issues, he got Tim himself as he missed Jess, our 12 year old black cat that sadly went missing in March 2021.
Unfortunately we simply can’t afford the treatment, and can’t bare the thought of losing him. I’ve never done anything like this before, but me and my family would be so grateful for any help towards Tim’s vets fees, we love him to bits and just want him back home with us.