The most I ever paid for a puppy was $800 (Rhodesian Ridgeback). The most I ever paid for a DOG is $2,000 for my oldest border collie. She was a trained sheepdog who you could throw out on any enormous field with any sheep and she'd go get 'em and put them wherever you wanted them. She was whistle trained, voice trained and just KNEW sheep. She could even herd lambs. horrible at sheepdog trialing because she wouldn't do something if it didn't make sense, but you wouldn't find a better farm dog. She's now retired and living in luxury being spoiled by my elderly parents. Best $2,000 I ever spent!!
It all depends on how rare, how talented the dog/parents/siblings have been, etc. I usually research the average price for that breed, find some bloodlines I like and then pick a number I'm willing to live with. I've got a border collie/australian shepherd mix right now that I got for free who is my freestyle disc dog. She's winning like crazy and I didn't spend a dime on her, I just saw the natural ability and trained her. I could sell her for a lot right now (but never would!!)