OK, OP, I owe you a debt of gratitude. This thread was perfectly timed because 1) I’ve been meaning to make cavaletti for some time now, and 2) I just moved my PITA cinderblock+heavy poles setup for mowing yesterday, cursing them the whole time. So upon hitting “Post Reply” earlier I got in the car and went to the Big Box home improvement store and made 3 cavaletti this afternoon. 
I formally officially retract the traffic cone idea-- I decided the cones will be too flimsy once you cut holes in them. Instead I used 5gal buckets like the above poster suggested. Mr. HH had a bunch of these in the shed, remnants from his escapades in container-grown tomato plants. I literally built three cavaletti in less than 90 minutes, including gathering the buckets and stuff, figuring out what tools I wanted, etc. I used a dremel with a rotary bit to cut my holes in the buckets–super easy. For now, I just zip-tied the poles to the buckets– will do something more substantial like a carriage bolt but for now I just wanted to test the theory, if you will. In their highest position, the poles are 12" high. You could stack 2 buckets to add some height. You can do poles flat on the ground by turning them 180deg. And there’s a middle ground with buckets lying on their sides–poles are about 4" high.
Oh, and weight? I carried all three at once out to my riding field. Though it took a few attempts to find the proper balance point so all three were simultaneously level-- Mr. HH said I looked like a bizarre, walking Calder mobile.
The PVC shards issue is something I hadn’t considered and will ponder. I’m thinking white or colored duct tape spiraled the full length of the pole would probably give fair amount of protection. And/or sliding in a wood closet rod/dowel inside the pole would give extra rigidity in the center and help prevent breakage/sagging without adding a ton of weight.
Can’t wait to ride them tomorrow. 