In the 500-800 dollar price range you are out of luck. Most items in that price range are Gen 1 which are made by Yukon
, and Night Owl. They have many items in that price range but none of which will attach to a Mil-Spec helmet
mount. They all come with their own form of head gear that the unit will attach to.
Best bet for Mil-Spec stuff is PVS 14's or 7's but that is $3,000+