Changing mine out would only take 5 to 10 minutes too. I basically just throw it down on the snow. If it wobbles because of a low spot, I throw one shovel full of snow in the low spot and it's done.
I was thinking about this and I think steel would be the best bet. This is kind of a crazy idea, but I would try to find an old circular trampoline on Craig's list. Use the legs and supports for the legs of your rail. Look at the supports for this old school tramp.
Two supports could be used for 2 rails side by side and they would take seconds to swap out.