Optics on the semi-automatic? It's always a question of what distance you're shooting and what it should cost. For close distances: EOTech, Aimpoint and Holosu...
Wilcox L4G24 NVG Mount ist im Moment sehr beliebt von US Spezialeinheiten (MARSOC, DEVGRU, USAF PJ, US Army SFG, usw.), aber das Original kostet um rund 500 USD...