I think you've seen EVERYONE's prices go up. It's a bit unfair to say "that one model has doubled" -- In that time, every iron set everywhere has roughly doubled.
I get your point; you felt like relatively it was a bit lower than others. Maybe that was true, but not by much. Go take a look at Callaway and TM and see what they're charging. I think you'll find that their adherents are roughly in the same boat.
It's also harder to sell your main cash cow, the 400 series, if you have a cheap alternative.