Yak, yak, yak. Here' s what I did and it' s cheap too:

2 landscape timbers
1 2x4x12
scrap plywood for a roof/floor
several sq ft of old carpet

Bury the timbers vertically into the ground about 36" apart. Cut the 2x4 into 3' pieces. Lag bolt two 2x4' s frt and rear on the bottom and two on top however high you want the target. Mount the frt upper board about two inches higher in the front than the the rear. This will allow a roof for the plywood laid on top to keep water off the carpet. Cut a piece of plywood for a floor to lay carpet on. Stack pieces of carpet cut about 12" thick/back and 32-35" wide (to fit between the timbers). Keep stacking the carpet to height desired. You can sinch down the carpet with thread-all on both sides or a ratchet strap. With a little elbow grease the target can be made for about $10.