I recommend Ed's Pawn in Stockbridge- the staff is much friendlier and willing to answer questions- not to mention, SPD charges the full $90 installed for night sights as opposed to the $56 installed that Ed's does. I bought at SPD once, and I have been an Ed's customer ever since.
Their LEO/MIL catalog with pricing can be found here:
(ETA- Oops, beaten to it, but I made it hot)
I would recommend that you call ahead and make sure that they have the model that you want- "common" models like the 17, 19, 22, and 23 are constantly in and out of stock. I had to wait a couple weeks for my Gen. 4 17 last year, but I was willing to wait for it rather than go back to SPD.
All you need is your CAC. Last time, I was in and out in about 20 minutes, including the night sight install.