I just finished my brass catcher. Not pretty, but I expect it to do the job.
Cost was about $30 when all said & done.
Copied wirecounter's idea of using BBs to weigh down the base. Also shot insulating foam into the pipe to keep the BBs from rolling around, and to strengthen the PVC.
I used 1" PVC pipe, but in hindsight I should've used a smaller diameter - either 3/4" or even 1/2" would've worked.
Net (as mentioned earlier this week) was from McCully Bike, 20" diameter for $7.
Still have two things to address: right now I just cut notches in the vertical pipe to keep the net from moving around, but I don't have any way of raising/lowering the net height. I'll have to measure the height from the bench the next time I go to Koko Head. Also, still thinking about ways to keep the back of the net open. It should work just hanging like it is, but might throw in some kind of hinged bracket later.