Just do a Google search, there are a lot out there. I have one similar to the chrome doughnut shpped one on the above link, but I am sure it was much cheaper than $25. The smooth chrome and doughnut shape makes it easier to slide on and off once you are hard. I have a 1.5" id ring which works great on my 5.25" pumped erection. Not tight enough if I am not pumped and too tight if I use chemical injections.
Sizing is important for a metal ring. Sometimes you can get three different sizes as a package deal.