How about $2.
I just bought a shaft collar at my local farm and garden store a couple of days ago.
It has an inside diameter of 1 inch, and it weighs about 3.5 ounces.
I removed the set screw, and smoothed it out a little with emery cloth. Then I worked enough of my head through; until I could get a grip on it and pull it the rest of the way. This is the hardest part, and a little spit can help. Once I get the head through I stretch my dick to make it narrow, and place the collar maybe a half inch up from the head. When I release the stretch, the collar stays in place perfectly, but it is loose enough to insure very good circulation.
I have some stainless steel o-rings ordered for the end of the week. They weigh .8 ounces each. so 4 of them would weigh about the same as the shaft collar. I think the o-ring will be easier to get on and off, and be a bit more stealthy. I think the o-rings could be worn anytime expect when sleeping, and stay on. They have 1/4 inch wire, so they shouldn’t pinch like a narrower o-ring might do.
The shaft collar is thicker, and it seems like under the right conditions, could come off, however it hasn’t in the couple of days I have worn it. I rode my bike and did carpentry work with it; no problem. I forget I have it on, but it is heavy enough to keep me from turtling.