I don't know if there is a debate or not regarding mutation vs. breeding, I do know that fur length is affected by selective breeding, but I do not know to what extent, such as if similar results could be achieved by selective breeding for sure or not. .com calls it a mutation. I have not done a lot of research on them, so I will be the first to admit I'm no expert on them.
Unless a chin had some other outstanding attributes, that is usually a low weight. Some people will not bred anything under 600 grams, some don't put weight into the equation. I did not look at weight until I began seeing the dwarf like faces time and time again, which according to them is common with the strain. Notice the flat forehead and smooshed nose, commonly noted in a brevy type animal, which is also usually large.
In reference to Jags comment though, I know very much how much work goes into working with a mutation, etc. BUT that is something you know going into working with a rare mutation. It reminds me of a recent deal with my SIL, my husband used to have a parrot, he gave her the parrot on the condition that if she sold it he got half. Well she sold it, and then my FIL was trying to tell him he shouldn't get anything because "all of the food and stuff" they'd put into her. She did not have a large cage, she didn't have toys or anything like that except when I brought some over for her, she was never to the vet or anything like that either. Basically all they bought her since he had her was food, the cheap walmart kind... Under this theory my horse should be worth much more now, because of all the work and food I've put into her. Also my car should be worth MUCH more than I bought it for, even though it was brand new, because I've put a lot of gas and oil and filters into it, not to mention a mass air flow sensor, O2 sensor, and new plugs, oh and tires... and car washes... and it's due for shocks, struts and brakes too... I'm guessing the value is running about 60K by now.
The price they get is because they can, it's a simple matter of supply and demand.