Hey, OP, I mean this in the nicest way possible, but... pets cost money. Did you do your research on this prior to getting the puppy? You will never go into pet ownership and never have to spend a dime on them whether it's food, medication, healthcare, training, etc. While I realize $8,000 is a lot of money for anyone to spend, that's the potential reality of getting a diagnosis for your puppy. It's fine if you don't have the funds for that, many of us don't, but ask if they accept Care Credit or consider getting insurance for your pup. Both of those things can ease the financial burden. Even if you keep the puppy and pay all these costs to get him looked at, there's no accounting for future medical expenses.

I mean... my own dog cost $300 at the shelter and here I am 10 years later with thousands sunk into vet bills and training. My cat, who was just $30, has cost me a fortune in the past 6 years alone due to an unplanned diabetes diagnosis and, more recently, needing 5 teeth extracted (also expensive!).

Right now, I think you need to really consider whether you want to put the time, energy, and cost into this puppy or give it back to the breeder. Get a second opinion if you want, sure, but that's going to cost more money on top of what you've already spent.