Originally Posted by Rowan

Give it to your father to tinker with. It's amazing how resourceful people can be when "experts" aren't involved.

I suppose it depends on where the tubing break occurred, but it could be internally sleeved with a steel or alloy rod or tubing, epoxied into place. Even if it broke at a join, expoxy might work, or if your dad has access to a MIG welder... well there is another solution.

The plastic bits also could probably be refabricated in metal instead of plastic. It might not have the adjustablility or foldability it used to have when undamaged, but you can only find out by experimenting. And if the experiment fails, you are no worse off (and won't have far to fall!)... but if it succeeds, you'll be back riding it again, and the expense will be worthwhile, even if only for the Wow factor.