Our small indoor has built a backstop of 12" wide carpet strips compressed between 2"X12" planks squished down with all thread every 4' and faced with cardboard. We have enough room for 10 lanes for paper shoots and we also have 3Ds we set up for our weekly competition shoots using the wall O carpet crap as a backstop. It works well and just about any construction outfit is looking for a cheap way to get rid of old carpet.

That plastic shrink wrap is the cats pajamas! It self heals and any dumpster diver knows Home depot, Sutherlands and just about all the other home repair and (boat dealers) pitch the stuff daily.

Plastic grocery bags stuffed into burlap seed sacks works well for individual targets and if you hang em right, the Product logo (ralston purina) makes excellent target reference points.

OR you could spend the big bucks and back everything with the Infinity Target blocks and make a wall out of them[8D] just kidding ouf course.