If you buy them directly from Millett they will be expensive.
Gun Parts Corp obviously picked up some business' inventory, when they got out of the business -- or took over a company like Brownell's stock, when they decided to refocus their product line.
I got a set of Milletts for my BHP, and they ARE good sights. I like the bright flourescent orange front sight.
(Mil-lay, I found, when I called them.)
I also have an AT-84S with has been customized. The front sight was a night sight with an tritium insert -- which disappeared. I tried to talk Millett into helping me with a front sight -- I was going to ship them the slide -- and they really weren't interested.
I later found that a Millett front sight on the E-Gun Part Corp sight would work, and got several, different heights, for about $4 each. (I needed a dual crimp staked sights to fit the AT-84S.) Had the parts in less than a week.