It's no Taj Mahal, but here's a sand target I built a couple weeks ago. Actually, I have more work to do on it yet. Once I got it to this stage I just had to start shooting into it.
It works pretty good. It is now messy with things I've thrown in to shoot at. Little plastic balls, clay pigeons, plastic bottles, etc. But, that's what I really like about it. Anyway, my total cost with materials and sand was around $160. I think that's a pretty good investment considering how long it will last. The mason sand cost $40. I used two layers of 23/32" exterior plywood for the back. Dimensions are roughly 4'x3'x6'.
As you can see, I shoot in a residential area and kinda overbuilt it just to be safe. I've also discussed it with my neighbors and they are all okay with it. They've been watching me shoot into my garage for years and wondered when I'd start shooting out back.
I also DO NOT shoot when anyone or their pets are out. Safety first.
Good luck with your target.