I havent dealt with these folks, but they came up in a quick search and had the cheapest price I saw...
http://www.del-ton.com/Aimpoint_Comp_p/op1004.htm
I have dealt with GG&G, and they are good to deal with. They often have deals running like this, which is a sight and mount combo. This may be the better route to go if you can use the mount on something else, or maybe even sell or trade it. I believe the ring alone is worth $175, which would make the Aimpoint $288.
I got my the Aimpoint M2 I have on my one AR from them in one of these combo deals.
http://www.gggaz.com/index.php?id=25...FQtN5QodAGtBJQ