I just spoke to a veterinary dentist. The person who answered the phone had never heard of this surgery, but the vet dentist herself said that it is very very uncommon surgery, but it is done.

She said that 6 months is too young to really worry about this, especially in a large breed, to give his teeth at least a couple more months to try to come in on their own.

If it eventually needs to be done, the biggest cost is for x-rays, to see if there are actually teeth THERE, and the surgery itself is not major surgery.