My dog Peyton's surgery (HBC)

My dog Peyton got out of the house and was hit by a car tonight! Unfortunately he has head trauma and will need surgical repair on his knee by an orthopedic surgeon tomorrow! The emergency vet (that I worked at for 8 years and was recently laid off from) needed 75% up front in order to keep him overnight . I have already spent $1500 just in ER fees for xrays and diagnostics and overnight stabilization until the surgeon can see him in the morning. We will be getting a new surgical estimate tomorrow once we know exactly what it will be, and again will need 75% up front in order for them to do the surgery. The surgery can cost anywhere from $3000-$5,000 and that is before the $1500 I have already spent.  Unfortnately I am currently unemployed and I can't come up with all of this money in such a small time frame. Peyton (Pey Pey)  is an amazing dog, my kids best friend and the best companion anyone could ask for. He is loyal, sweet, and much more than a dog, he is part of our family! We are truly devastated! ANY HELP WOULD BE GREATLY APPRECIATED!