Mudd,
If you have an old tarp you can buy four bales of wheat straw. Buy the ones with the nylon strings. Stack them two wide and two tall. Stack them on the cut edges of the straw.
Place your tarp on the ground where you want your target and fold the tarp to be as wide if not a little wider than bales. Also buy one can of the expanding foam. Place two bales width wise facing your shooting lane on the tarp with the length of the tarp towards your lane. When it's over you want to wrap the bales like a burrito. When the two bales are facing your lane and side by side (tip to tip) you can then spray a layer of foam on the tops of the ground level bales and then stack the last two bales on top of the other two in the same fashion. The foam will be a sealant between the bottom two and the top two. Then take the tarp and wrap the bales to keep them dry. Let the foam set up, about 24 hours, and that prevents arrows from going through the bales at the seam. Do the ends too if you have enough foam.
Four bales - $16 roughly
Brand new tarp - $20 roughly (use an old one then get the new one to replace the intent of the used one)
Spray foam - $5 roughly
If you go three high by two wide you might need post supports on the back side of the bales to keep it stable. You could just go three high.
After you shoot up the bales or they start to rot you can use the to plant tomato plants in....a bale garden.
This is great for field points. Broadheads might cut the bale strings.
Here's my three bale tarp covered target stop.