You like many have been scammed. "Pet Boutiques" that sell puppies are selling you puppy mill stock. You could have gotten a beautiful healthy pup for not much more than what you paid for this poor little guy. Many good breeders sell their pet stock for that much. It is a shame that people get taken in by people like this and many of the puppies do die. I am amazed that your puppy survived this long with that amount of vomiting. A small puppy dehydrates quickly and when their blood sugar level goes down they die. There is a lot of good information on YT about puppy care. Read in the library section and the "sticky" area at the top of every forum topic area.
I don't know where you live but $1000 a night for a puppy that is only being hydrated is kind of high. You might want to consider checking around for more reasonable medical care if you are looking at an extensive stay. I'm not saying look for cheap care but more reasonable but reputable caregivers.
The dog food the Boutique gave you is bad stuff. You might want to get information about better dog foods. There is a lot being found out about the big pet food manufacturers. They use way too much grain and low grade ingredients. Here is a link to a site that gives you rating of dog food and explains the ingredient lists. It's a start anyway. Never change a puppy's food quickly. It should always be done gradually over several days. If your puppy makes it the vet may send him home on a special food to keep him going for a while.
http://www.dogfoodadvisor.com/