You could steal them from the local gun store, I did that once by accident went back into pay and was told to keep them. The guy ringing up my stuff forgot to add them.

I just buy Birchwood Casey Shoot-N-C 6-Inch, https://www.amazon.com/Birchwood-Cas...=ATVPDKIKX0DER

I get 3 uses which brings the price down to .08 cents. I either stick them to foam board or poster board from dollar tree. after 3 uses i have spent something like .30 a target. IMO .30 for a target you can actually see at 100yrd isn't too bad. Also the targets can often be pealed of latter and stuck into a note book for reference.