There was some discussion about Johnson Resonators here last year. I can't get the "forum search" to respond, but you can try a forum search for "Johnson Resonator" in the body. There has also been some discussion about them in the newsgroup
rec.music.makers.guitars.acoustic. You can try a dejanews search for Johnsons in that group.
They are made in China. The general opinion was that they are a good buy for the money. They are even better if you spend an extra $100 or so and get a new (National?) cone installed.
As far as price is concerned, to get an idea look at Elderly or Mandolin Brothers (sorry, I don't have their website) and see what they charge. They both usually offer the best US price.