Find a scrap metal yard and ask if you can look at the barrels of scrap they get from metal fabricating and machine shops. I've found disks from 2" to 10" dia., plates of all sizes, and cut off sections of steel pipe and steel angle and channel. They sell the stuff by the pound, so you can afford a lot of it. 1/4" thick steel is fairly light and easy to drill, but round balls beat it up in a hurry. 3/8" is better, and 1/2" will last a long time shooting it with a ML or a handgun. Cold rolled or mild steel is fine, you don't need armor plate or anything fancy with ML. You can get the folks at Home depot to cut heavy chain into sections about 6" long, then have it welded to the targets, or drill holes in the targets and use 3/8 or 1/2 inch stove bolts. Use links sold in the hardware store on the other end of the chain, and hang them on rebar on steel fence posts. I use large eye bolts through holes drilled in the plate on the fence post to hold the rebar, then drive the posts in upside down.
If you want these things to last you have to make everything very sturdy. A .54 round ball packs a big punch even at 150 yds, and if you try to hang the targets from tree limbs or 2x4 frames they won't stay up long.
Finally, if you want to see the things in the woods, paint them white with a black center. Buy several cans of el cheapo spray paint, and plan on painting them often. We've tried bright colors, including dayglow orange, and these work under some light conditions and become durn near camo under other conditions.
Shooting steel is addictive--I have very little interest in paper targets anymore, except for sighting in and load development.