These sights have been on the market for a while now, but I recently stumbled upon them while shopping for back-up sights for my new AR-15 build. At under $90 the A.R.M.S. #71L Series back-up sights are in the same price range (although slightly cheaper) than the Magpul MBUS Gen2 Sights. They mount to all universal 1913 Weaver style rails and are made out of durable metal-reinforced polymer and sit just .610″ high when folded down. Just a note, you can’t mount these along with other polymer sights and accessories on gas blocks.
Visit Armsmounts.com for more info, or visit Amazon.com to purchase a set of the A.R.M.S #71 sights.