Fill a garbage bag with plastic wrap, lumber wrap....tarps, etc. When it's shot up, put it in a new bag. I'm on my 3rd year of the same filling and several cheap contractor garbage bags later....still winning.
I can shoot long range broadheads into them and CT them out without feeling like I'm destroying a bunch of $$.
Ive had great luck with coffee sacks (burlap bags) stuffed with shrink wrap. i asked around and a local box store offered to keep all their plastic wrap from shipments for a week for me. stuff the burlap sack tight and wire the top shut. ive shot thousands of field points into it and it looks great. it creates about a 2ft x 3ft target for those of us not as gifted as yourself at longer shots. stuff it in a fresh bag once a year for $3.