JRM,
Cost of a dog or worth of whatever you buy is a very complicated thing.
Paying more for something to some means getting a higher quality whatever, simply from the cost.
I've got a $5,000 dog you only paid $1,000 for yours so mine must be 5 times as good, you see the point.
What you expect to get from a started or finished dog and what the next ten guys expect to get are going to be very different.
You need to have a list of questions and get honest answers about each of them from the seller.
1. Timid, gun shy, afraid of loud noises?
2. Does it listen to basis commands?
3. Load and ride in a truck with no problems?
4. Engage a coyote when seen or sent after?
5. Does it decoy or just chase to catch the coyote?
6. Have to have an elec. collar on to correct behavior?
7. Does it hunt trash off the lead.
8. Trained to roam when on stand or sit next to caller on stand?
9. Will it track and find downed coyotes?
10. How much aggression does the dog have in it?
11. Does it get along with other dogs and people?
12. Health, bloodline, physical shape.
13. The country you will be hunting the dog in?
These are just a quick dozen or so I can think of off the top of my head. Each one can be a topic of discussion because everyone wants something a little different. Each question has a lot of grey area to be talked about.
If you find one that meets your needs and does the majority of them to your approval my next question would be "WHY" are you selling it?
As for the amount, if you find one, it is usually going to be a pure luck deal and you better snap it up. A dog being sold because of a number deal, reducing from 2-3 or something similar, or an older dog being replaced etc. A relocation, a financial deal, needs money etc.
Be very careful with sellers who have lots of dogs all the time because IMO it is not possible to train a huge number of quality started or finished dogs by a single person. Simple logistics. Possible but rare.
Also a dog trained with another dog thru out training may not be the same dog when sent home with you and then hunted alone. Some dogs are very good followers but not very good leaders. Then can get in real trouble very easy without that backup that can ruin them.
It takes very little skill to make a dog want to bite, wool, chase. All you do is cull dogs that do not show aggression. You then reward the aggressive behavior and your dog will want to catch and chew just about anything. To some this is a decoy dog, not me.
In a nutshell you need to ask the right questions and figure out what you want it to do. Then find a seller with similar views and a dog for sale.
Price? A finished dog easily in the $5,00 to $10,000, they will be priced similar to good cattle or sheep dogs as the jobs in some respects are very similar. Older dogs $1,000 to $5,000 depending on age and the shape they are in. The trick will be even finding a marginal dog in the 2-5 year range with experience unless it is totally worthless. Very, very rare to come up with a good dog for sale.
I think sometimes we take good dogs for granted and undervalued until we don't have one. Especially ADC wise.
JRM I assume you will be a recreational caller using it only during the fur season for the most part? That time of year you need less aggression in a dog. IMO. You may need it to be more of a pet? May need to stay inside? Live in the city? Who knows what, you will have to weigh all the pros and cons.
You may find a freebee like John stated, I have had a couple. Had lots more that I wasted time and money on. Also had dogs that came from the best of bloodlines and were not worth the high dollar price. Whether it be in pups or older dogs. It's always a crap shoot with dogs. It seems some people connect better with dogs, some people are more honest than other people, and some sellers have the ability to relate before the sale to you and your needs and if it's not going to work say so.
I wish you the best in your pursuit of a dog and hope this post helps. It's not something that one post can anwer all the questions or opinions on but it can get a person thinking! Best of luck to ya.