Not an ACOG, but a good budget option. There are only 4 available at the time I posted this.

It's the cheapest I could find ($150 cheaper than Bocrap had them advertised last month).

Trijicon, Inc., the leader in the development of innovative, self-luminous aiming systems, has introduced the industry's first triple-illuminated sight. A failsafe firearms system that provides a fully illuminated reticle that's easy to see in virtually any lighting conditions, including partial or total darkness.
Trijicon Fiber Optics - Trijicon's ultra-reliable fiber optics system adjusts the brightness level and contrast of the reticle to the available ambient light. The chevron-shaped reticle presents a crisp, clear aiming point, even in the brightest light.
Military-Grade Forged Aluminum 1-Piece Housing - Forged 7075-T6 aircraft aluminum alloy 1-piece housing provides for a nearly indestructible sighting system.
Battery Illumination Switch
Trijicon's Tritium-Illuminated Reticle Thanks to Trijicon's tritium powered phosphor lamp, the reticle provides a distinct aiming point, even in total darkness.
Broad Band Anti-Reflective Coated Lenses Allows optimum light transmission and optical clarity.
Threaded Objective and Eyepiece Enables mounting of various adapters, secondary mounts or lens covers, including flip covers.
30mm Tube Allows use of 30mm rings and scope mounts.
Waterproof - Completely sealed and waterproof to a depth of 100 feet /30 meters.
Adjustable Windage and Elevation - Sealed external windage and elevation adjusters. (Normal adjustment range ?1.25 degrees.)
On-Call Battery Backup - Trijicon's advanced battery system provides a backup light source for a crisp, luminous reticle at all times.