How to make 3" concrete "legs" via reusable casting structure?
Yes, you could use 3" PVC schedule 40 pipe such as This one from The Home Depot.  Cut it to length, then cut it lengthwise on one side and use duct tape to hold it together... This single cut will keep the round shape and when it has set, it will give you the ability to flex the pipe enough to have your cast come out.  I would not use a PVC end-cap, but I would just make a duct tape one.  Cutting ten foot length pipes will make you six molds per pipe @ ~$9 per pipe.. 100 casts in 8 batches for &lt; $20.