This isn't practical for any of you most likely but I bought an empty Morrell bag like the photo above. I have llamas and have a bunch of fleeces stored up. I stuffed a dozen in the bag and closed it with zip ties. Its been the best target I've used.
For less than $5 a bag, burlap feed sacks do the same thing. Though not as weather resistant, I shoot one up and need to replace it long before it rots from the weather.
I prefer the burlap to better mimic an actual shot on a deer or elk since they usually don't have bullseyes painted on them Either one of these setups are simple to put together and are relatively lightweight for portability...