Do a seaarch on targets, we have covered this extensively. Suggest you watch out for some old swing-sets for hanging steel targets, they are usually free and work great. We shot some standard steel plates today at 500 with two or three different .308 Win. bullets. Essentially the 1/4 plate did not do well, significant divots and concave shape after a half-dozen hits. 3/8" did much better, very slight concave, no divots. 1/2" was fine, withstood the hits very well.
AR500 is the best but not needed at longer ranges depending on the caliber. We practice a lot with .308 Wins and they will not beat up steel plates at 700. I have seen big plates of soft steel go concave from hitting them with .338 Lapuas, all you do is switch them around and shoot the bend out.
The target Shawn mentioned is very good. Also check out www.lvsteeltargets.com
for some nice AR500 reactive targets that are affordable.