I was able to rent a car when I was 20, just for a weekend. It wasn't the world's easiest thing to do- my dad had to add some coverage to his car insurance, which I was a secondary driver for, and then fax proof of the insurance to the car rental company, plus I had to pay two extra fees- one for being under 25 and another for being under 21. But I managed it. Since it was only three days, it didn't actually add up to as huge a bill as you might imagine it would. I had to drive from college to a friend's wedding, so it was worth it to me.

Whether you could go through all this trouble AND rent a hybrid, I don't know. It was hard enough when I had no particular car preference. But doable. If you feel strongly enough about it, you should call a few places and at least see how much it would cost.