Certain Shakespeare rods are ok. I have 2 of there graphite Excursion ones that are decent and are pretty light. They still don't compare to a quality graphite rod but for $15 to $20 you can't go wrong if you need another rod.
There is a thin walled PVC you can buy. We buy some occasionally for work at out local irrigation supply store. Its probably half the thickness of regular schedule 40 PVC. You can always spray paint it black.