It depends on the quality of the dog and the training it has so far. You could be looking anywhere from $3,000 to closer to $10,000. Especially once you factor in pedigrees and health testing, plus the potential ability of the dog at hand. If its trained for a BH as its maximum potential, then you'd be looking at a difference price for a dog with BH level training that has potential for National level competition.
Right now, average price for well bred working line pups out of proven parents in the US is between $1500-$2500. Weighing that against the cost of an adult dog with some training and potential health testing already done, you can see where the cost comes from.
Is he trained to do other stuff hence can easily pass a BH, or has been trained simply with passing BH and continuing in mind? I've seen a retired police dog get his BH so he can go on to IPO..just because. He was an accomplished Border patrol Dog. And worth a ton of money (for a dog IMO). Age, other abilities, and pedigree factor into price a lot from what I have seen. I guess if someone wants a dog that can definitely do what they want it to do, they wait and pay for an older, established, and proven one instead of possibly getting one from a litter that did not get the genes they need to compete or work.
Years ago when I was looking for a service dog for my autistic son, a good prospect puppy was about 1800 or so, with no guarantee he would ultimately have the goods. Conversely a trained ready to go one was 10 to 15k.