Not sure if it's worth the extra 200-300 bucks, but on ebay you can get 60mm-88mm carbon tubulars for 350 bucks shipped, clinchers for 400-450.

Then it's yours forever.

Or if nothing else, wheelbuilder.com sellss disk covers for 95 bucks for your rear wheel. Not going to get any bigger bang for the buck regarding wheels than that.

And a pair of continental GP4000s with latex tubes will probably be just as if not more effective at gaining speed (via significantly reduced rolling resistance) than a regular 50mm carbon rim, meaning you could take that rental money and invest in the tires and tubes and be just as, if not faster over and over and over again.