I use real estate signs for target stands (purchased at estate sales). Mount cardboard, and cover with butcher paper. You can buy butcher paper in bulk and the bright white makes it easy to spot your bullet holes. If you don't want to invest in a roll of butcher paper, poster board also works great and it is much less expensive at Dollar stores.
I use Shooterscalculator.com for ballistics. It is worth your time to understand Point Blank Range. Ballistics wasn't intuitive for me when I started shooting, and running the numbers really helps.