yikes!! that a lot a dough. I've never seen them remove the old plaster. I have seen several pools redone, including my own, and they acid wash the existing finish, chip up any loose spots, undercut around the tile then apply the new finish on top of the old. Is yours that bad, as in all loose that it has to be removed? If so, I would think you could do that part yourself. My buddy just re did his pool and he did the new tile his self. He still paid around 2,800.00 for a 20,000 gal pool for Diamond Brite (although he got scammed and got another knock off product instead of Diamond Brite). For that much money, I would do what you can yourself but leave the actual finishing to a pro.