I figure the BCM Gunfighter is the most recommended piece of kit for my situation, but I'll gladly consider other less expensive options. I'm wondering if the medium sized one would be big enough to rack it from the left side? I don't want it stabbing me in the gut when the gun is slinged, which is why I've never considered replacing the standard charging handle before, but now I need it to stick out far enough that I can charge it while my NV scope is attached behind my Aimpoint.

not really cheaper. but, I love mine.

Yes, the Mod4 will allow you to use your left hand to operate the handle. I like mine a lot and I don't think you will find a better handle cheaper. WCArmory has them for under $40 but didn't check shipping prices.