falconry2
You could use the Shrink-Wrap Poly film that is discarded from pallets. You need to get a lot of it and compress it down and then put that into a burlap bag large enough to serve as a target. Other packing material that would work is foam sheets folded and stacked tightly. Again, it would need to be compressed and tied or secured in a box that is serving as the target. If you use the foam, you want the folds as the exposed target, not the "field" side. It would look like a phone book and you shoot at it like you would shoot the page edges opposite the spine. Commercial targets stack foam and bind it tightly, and you shoot between the stacked sheets to ease the extraction.

stupidnameshaveallbeentaken
Hard to beat the price of 3 straw bales and a piece of cardboard. But I'd recommend at least 6 so you can go 2 deep, and if you have the extra $5 a few on the sides since you're beginning. Stray shots will be fairly common.

skip
foam insulation boards atleast 8 inches thick i stack 1 inch thick pieces and duct tape them together

jracciato
Straw bales are cheap and effective for the poundage you are using. Don't use broadheads with it, as they can be a pain to get out. I have used them for years with bows in that range. The don't, however, stop crossbow bolts from a 150 pound crossbow. They go zipping right through and hit the house. Leading to a thorough scolding from the wife. It was a small hole... It didn't go all the way through. I don't think she needed to get THAT upset about it...

thinkingblade
Well, if you are handy enough, this is what a friend of mine and I did to set up an archery target. First, we set up a couple of saw horses with 2 x 4's a couple deep acting as a base. In the ends of the front and back 2 x 4's we drilled holes big enough for a 1/2" threaded rod to go through - total of 4. Then we stacked phone books pages out, 2 sets deep, spines back, and probably 4 feet across, and 4 feet high. Then, because we had foolishly already set this whole thing up on saw horses, we put 2 x 4's like the ones on the bottom on top of this pile then got up on ladders and with big flanges on the threaded rods tightened the whole pile down for all we were worth. I mean we cranked the heck out of those flanges with long wrenches until we had those books compressed hard. Then we started shooting. In fact, you can stop a crossbow bolt with something like that - although contrary to popular myth cross bow's, pound for pound generate significantly less energy than a compound bow. Further I was shooting at it with a Browning Mirage set at 93 lbs shooting Easton XX75 2315's with a field tip and they would barely go in more than a few inches. It would stop carbon's as well. Periodically we had to get up on ladders and crunch it down again as the books started wearing out, but it lasted for several years. Good luck, Thinkingblade