My buddy made a compressed cardboard target. He has it outside under a tarp and it has lasted 3 years now. Pretty easy if you have access to enough cardboard. It's cardboard sandwiched between 2 boards with threaded rods in each side to compact it. Then you can dress up the outside how you like, even place it on wheels. Here is a very similar one from archery talk. You can use ratchet straps instead of threaded rids also.
