I've DIY'd all types of targets ranging from old clothes to sand to styrofoam etc etc.
The best I've found and cheapest for field points is using construction grade garbage bags which you can get cheap 20 in a box and using plastic wrap or bags. Where I work, I can get unlimited bunch up shrink wrap plastic they take of skids of product, when these are bunched/rolled up, they are quite strong. Take a garbage bag, cut out cardboard from cardboard boxes (get them at stores or grocery stores) and I put them on the bottom so they sit up straight and don't fall over and then I put a piece in front and back inside the bag, now stuff the center with the plastic wrap, tape it with duct tape and you're good to go, believe it or not, these will stop broadheads too and they are super light to carry around or transport to a range, I've shot it with SlickTricks, Carbon Express Quads and Mechanicals and they stick just find, the fixed BH's will go through in some cases but only about 4 or 5 inches through. The only problem with this target and BH's is that you will chew through the garbage bag pretty quick but the plastic inside will last forever. When you make a new one you're really just changing the garbage bag and cardboard, the plastic you just restuff with the same and it will resposition on the inside so there's never a "tunnel" from previous sessions.
See photos below...
For my 3D target, I made it so the body is actually two boxes side by side, the vital area where I shoot is actually a box filled with spray foam, the other box is either filled with sand or magazines. Spray foam is a good BH stopper but spray foam is not cheap and if you don't let the inside of the box you fill dry long enough, it will stick on your BH as it goes through and you'll spend a good 15 minutes cleaning the goo off (I learned the tough way from being too impatient to let it dry
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If you look at my set up, the back of those targets I use boxes that's filled with old magazines, they stop anything! I wouldn't use either carpet or magazines for BH's, hey work perfect for FPs, they will stop it perfectly but if you're BH doesn't penetrate through then you won't be able to get it out at least not the way I've made mine. With carpet filled targets, fixed BH will get caught on the carpet fibers and you won't be able to pull it out, same as using old magazines. It's ok if you it shoots through, you can just unscrew the broadhead and pull the shaft out easily.
I found the expandable foam the best for fixed BH, you can pull it out cause it's soft enough but everytime you do, you'll shred a bit of foam out. When it gets bad enough, just fill it with some more foam, back to new.
Mechanicals I wouldn't shoot at any target without tying the blades down or you're be breaking a lot of blades. I use either dental floss or fishing wire to loop over 5 or 6 times to lock the blades, seem to work perfectly and you can use it on the garbage bag targets no problem, even pulls out like a field point.
I shoot three different types of broadhead, I dedicate 1 from each pack of 3 for practicing on my targets and the other two are used for actual hunts. If my practice BH shoot good, I have no doubt that the new ones will shoot as good if not better.
Hope this helps, good luck!