I made one out of those interlocking foam floor mats. I used the cheapest ones from home depot ($20)and cut them in half and then stacked them between two boards like this:
I didn't do mine quite as tall, but it's worked good thru a lot of arrows. What' nice is when an area starts to get too worn out, I can just move the worn out pieces to the top or bottom of the stack and put less worn out ones in the middle. And when it gets real bad, another $20 and I can swap in fresh layers pretty easily. Swamp and Stomp did a similar build too, and it's worked great. I do like the wagon wheels above, now I may need to do a modification to mine!