We don't know, because there are many costs that are associated with this.
You will need vet paperwork. If your friend is getting the puppy and transporting it, they will need to do all of the paperwork and have their name on it. The dog will be legally theirs. How much a vet charges for this paperwork is not something we can say. I would not get this paperwork from the breeder, take the pup to the vet to be sure that the pup is in good health. This is standard pet care no matter where you get a pet from.
Contact the airlines that will fly a dog, and ask what their policies are, what paperwork will be needed, and then the cost. I have heard that American Airlines has a great pet program. Because of the length of this flight, I would not keep a dog in the cabin. To have an animal in the cabin, they have to be able to fit under the seat in front of you. This is a tiny amount of space for a dog. The dog will also need to place to pee and poop, and you can't take the dog out of the crate on the flight so the dog will be sitting in its own waste, which will smell, bothering other passengers. Put the dog as cargo with a larger crate and puppy pads.
Then there is the issue of ownership. For your friend to get the pup over here, they have to claim the dog as theirs. You will need a written statement from your friend surrendering ownership to you. I would talk with a lawyer about this just in case. Usually a private sale of items or pets between two people is no big deal and does not require paperwork, but because the dog is in your friends name with the airline, and the breeder in Germany, its a good idea to get you legally recognized as the owner.
This is costly in time. This takes a lot of time to do and to plan and to make happen smoothly. It might cost a bit more money to buy a dog over here, but you will be paying for the convenience of it too. Plus Germany has crazy high sales tax, and the US dollar is weak compared to a German Euro.