I made about 20 of these w/my cub scouts last summer....just have the store where you are buying the one long pipe cut it into small sections, buy some connectors and let the kids create their own. We had several different kinds made and they had a blast going to "war" afterwards. My own kids have their 3 still up in their rooms and will even continue to interchange "parts" as they think about new designs.
For 10 boys, we made 2 each (a small one, a large one). It took only two of the long thin PVC to cut into sections and a handfull of connectors. I bet it didn't cost me more than $7 total for the 20 we made that day. No glue was used so they could "refine" their designs.