It's nice that Disfarmer is back in the news. I remember back in the '70s?... '80s?... when a big exhibit and book helped give him a major art-critical reputation. For a while I think he was right up there with Atget, another mystery man "discovered" by the art community after the fact, and since then I think it's been up and down in cycles. This new find of vintage prints, with its interesting back story, should be enough to spark the market again.
His best work IS brilliant, very somber and a bit confrontational just in how plain it is; it has a stillness to it, a sense that time had stopped forever when he pressed the shutter. (Of course he didn't use a rangefinder camera; one account I read said that he had his portrait camera built into a wall in his studio, so he could leave the subject to fidget by him/herself in one room while Disfarmer disappeared into the other room to take pictures.)
As to $30,000 being an awful lot of money -- well, it is, but keep in mind that that figure was for the vintage prints -- the ones made at the time Disfarmer was working. The thing about those is that there's a finite supply -- there will never be more of them than there are right now.
It's just like shopping for old cameras: If you see an ordinary Fed 5 or Canon 7 or whatever at an outlandish price, you pass on it because you know you'll have lots of chances to buy another just like it for a more reasonable figure. But if the camera is something really rare -- say, a Minolta Sky or a Contax VK27 -- you have to factor in the likelihood that you may never have another chance to buy one, so if you want it and have the money, you have to pay the asking price.