Ok, now what do I do??

This beautiful big baby is laying on my living room rug.
Katie, Nichole a little help here.
While driving home my friend Shannon and her 3 kids, one is 9 the other are babies,saw this dog laying in the grass. She could tell he was hurt. He looked a lot like a dog she used to have. After she got out and looked closer she could see it was a problem with a back leg. She called me with a, this is what I found now what do I do. I jumped in the car with the 5 kids I had and drove to where she was.
He was having great difficulty walking, almost dragging a back leg. I gave him some water and some dog food. Yes I had a baggie of dog food in my car. We had taken Hutch with us to swim and I brought his food. The dog was very hungry and thirsty. No tag just a collar. I felt along the injured leg, didn't seem to be broken but when I got to the hip he turned and looked at me like "please stop". I think his hip is dislocated. After some discussion, knocking on the surrounding doors I put him in my van and we took him to Hutch's vet. 2 women, 8 kids and an injured dog waited in the exam room for the doctor. This could be very long, so I will sum up.
The estimated medical cost are $500-$700. We have no money for this. We have already paid $100. I called the KY LAB Rescue and they sent me to LABMED.org. The application for assistance was approved and I am just waiting for the vet to call and say bring him in. We have posted flyers, knocked on blocks and blocks of doors and a found ad will be the local paper tomorrow. So if we find the owner they will have to pay LABMED back for the medical care. If no owner is found, Shannon and I are not quite sure what we will do. The kids do tho, KEEP HIM!