Recall that we used to get DDM boosters with 8 miniatures for less than $10. Yes, it has been 20 years, but according to the consumer price index we've only seen a ~60% total inflation over that period ... meaning it would be fair to see a similar product for $16.
Some of the price increases come in changes in petroleum costs, labor costs, etc... The paint on these minis is a little better. And you get more of the larger figures here than you would on an Archfiends booster. But does all of that add up to $84 in excess price increase?
It seems more likely that they're comfortable selling much fewer miniatures at much higher prices.
I think someone is going to find a way to mass produce RPG miniatures that are prepainted and cost efficient. When they do, if they can get a foothold and start to provide real compeititon, we'll see how the prices change.