I have the luxury of having my own 150 yd. range in my pasture, but we use steel railroad tie plates with a base welded on, and sat on top of posts, at 100 and 150 yds. for reactive targets. Durable, and cheap.
Don't try this too close though, a couple of years ago, I had a large fragment of a .40 splatter back and knock a really big hole in my ear muff from 15 or so. That gets your attention in a hurry.
Someone was watching out for this old fool that day!!!!!!!!
Tom