Help carti after being hit

This evening my sisters dog carti got hit by a car, they went completely over him with both wheels and caused pneumothorax along with multiple contusions on his lungs, a dislocated hip and abdominal trauma. This dog means more to my sister and I than mostly anything in this world, he is the most sweet caring dog i have ever met and he truly has helped save my sisters life as she has struggled with depression & anxiety throughout her college years. All carti has provided to this world was joy and love and his love is felt so hard and he loves so hard even if it’s not expressed verbally, his story does not need to end here, it shouldn’t end here so any help would mean the absolute world to me and my sister. The vet is estimating around $4000 for him to get oxygen therapy over the weekend along with keeping him stable to see if he can go into surgery on monday, if he stabilizes the surgery could cost up to 4000 aswell and that’s not even including the extra costs of x-rays and on top of the 2k we have already spent.