I would like to mount an Aimpoint on my Bushmaster and would like it to cowittness with the cut down carry handle site that is currently attached. I have been looking at some of the mounts online and they are rather expensive. Any reccomendations for a site mount around $100? The Aimpoint railgrabber and spacer seems to fit this criteria, any experiences would also be appreciated. Thanks guys.

You get what you pay for.  The "good" mounts will hold zero, will not shake off after rapid fire, and look nice to boot.  Getting a "cheap knock off" will just cause you aggravation.