Ballpark Pricing of started-intermediate-Finished, last few years they've been low
Started (marks, OB FF CC) ~1800-2500
Intermediate (Started + runs blinds, water-forced etc) ~2500-5000
Finished dog ~ 5000-9000 (female = more, Age younger =more)
Then again the price really depends on the dog, pedigree, health certs, age, titles etc. add to price. I've seen them go for a lot more, some for less.
IMO talent & skill set sells a dog. I've seen dog with titles go for a lot less than those who have never ran a test. It basically comes down to can the dog do the job, the buyer wants them to do. Also ask for a health guarantee, most sellers will offer you one on a young dog until they can get their OFA's, on an older dog a time-period for you to do the testing, or get vet certification. Still depending on age, you'd most likely know about any affected health issues by now that's one reason to buy a started dog. CNM is very early, EIC training should've shown it, Hips dogs can't move on well on bad hips-elbows. A simple vet check can ease your mind with heart-lung issues, overall health, movement etc. High money testing might not be necessary if your looking primarily for a working dog and not a breeding prospect.
If the dog is sound and does what he says $4000 is a good price. On a (22mt.) dog for this price, I'd be looking for marking ability (harder doubles-simple triples), hunting instinct, temperament, simple handling (good but, not excellent) water & land. If the dogs got that and hunting experience, I'd consider it a very good buy.