The school where at which I work recently dropped our prices due to reduction in fuel cost. Depending on the plane, it was anywhere from $4-$12/hour. Rates may drop a little more if fuel prices continue to drop.

Our cheapest plane still rents for a little over $100/hour, however. As others have said, there's a lot more cost to operating an airplane than filling the tank. Insurance, scheduled maintenance, unscheduled maintenance, payments on some aircraft--these things add up.

Learning to fly is expensive. I suppose there are some gradations of expensive, say, Somewhat Expensive to Very Expensive to Crazy Expensive (seriously, people, stop getting your PPL in an SR-22), but Cheap it will never be.

And be careful the seductiveness of dry rates. Sometimes they're a good deal, other times not and, regardless, be sure to budget for your fuel costs.