Just bought a Bushnell AR 1-4x24mm illuminated reticule with Throw Down PCL. Currently sold for 349 with rings at Al Flaherty. May be overkill but will switch it on a upcoming AR. In the mean time, lots of fun on the ISSC MK22.
Depends if you want a dot or some magnification, and what affordable means for you. Compared to the crazy high end stuff CGNer are putting on their toys, I consider this one affordable.