Oh, been there, done that. Sorry you have to go through it. 
  Have you checked out Care Credit? The surgical specialist may have the information and application. Care Credit offers FREE  interest loans for a specific time--usually 3-6 months. The veterinarian chooses how much the clinic will pay Care Credit for your business. That's what we did and paid it off without paying any interest.  Dentists also carry it.
We have a super athletic Belgian Malinois who tore her cranial cruciate ligament while working for military. Since they couldn't be certain she could continue active duty they put her up for adoption--she was only two years old. We fell in love with her and took her to a specialist and had a TPLO done. We had a stem cell injection done in the other knee as that one was mildly injured to hopefully prevent surgery.  The stem cells healed the one knee and allowed her another 1 1/2 years with no problem but we still had to have another TPLO done on that one. Now both knees are EXCELLENT but we paid a total of $11,000 for both knees. 
  It cost us a little more than usual because of the stem cell treatment and to have the plate removed because she got an infection the second time around.
The biggest hassle was the recovery. Ugh. We had to put her in a covered pen (4x4) to limit her to just a short leash walk to go out to potty for a month, then increase the time of the walk for the second month slowly increasing excercise if she handled it without pain. She also no longer had to stay in the pen all the time.  After three months she could do most things but not allowed to go full speed for long or jump too often. At four to six months--anything she wants as long as she stayed sound.  Now, she runs at a gazillion miles an hour, jumps, catches Frisbees, runs two miles, etc., no problems whatsoever! 
 Worth every penny to us for this magnificent family member 
Big dogs typically need to have TPLOs if they are active and athletic as they will invariably injure it again and again and arthritis occurs in the joint.  Sorry