This one is the lower profile version not like the eotech styled one. I got it for $150 used from an ebay seller. It's in pretty good condition but it has the remmy shotgun mount. I see where I can take that off but I have no idea what kind of mount to buy to attach it to my M&P 15 rail. Any suggestions?

Not sure about any specific mount that will fit the base of your sight, but you want a mount that fits the standard Picatinny (MIL-STD-1913) rail on the M&P-15 side...

~Dan