Check out Brownell's. They carry most of the brands that have been mentioned. I have Mep adjustables on my Gold Cup; Trijicon fixed on my Glock 21. I can't tell any difference in brightness, and they have the same 12-yr. warranty. Since you're interested in adjustable, that limits your choices. If MMC makes a sight for your gun, you couldn't go wrong with them.
You can get "dealer" discounts at Brownell's by opening an account online and answering the question regarding "being in a related business that doesn't require an FFL" in the affirmative. (Or, you can just pay suggested retail, if you prefer)