Back in October I posted this in Sandbags, the ultimate in stationary ballistics protection? Might also work for your situation (at a reasonable cost depending on your fill availability), if you have access to Home Depot.
“In reply to: Sandbags, the ultimate in stationary ballistics protection?
Possibly the Ultimate sand bag! http://www.homedepot.com/p/WM-Bagster-Dumpster-in-a-Bag-775-658/202228840
2.5′x4′x8′ for $29. Need a serious barrier (semi portable)? Would require about 3 yards to fill it, and weigh ~6-9 Klbs depending on the fill, but would probably stop an AP 50 BMR!”