While costs do vary over time, natural gas grilling costs only about 1/3 as much as using propane canisters. This cost savings is in spite of the fact that propane actually contains about twice as much energy as natural gas. Nevertheless the cost difference between these two grill fuels more than offsets propane’s efficiency.
If you already have natural gas to your house, a natural gas grill will be cheaper to operate compared to a propane grill. And if you pause to think about that, it makes sense. If you already have natural gas service at your home, you wouldn’t purchase a propane powered appliance even though it had a lower upfront cost. Its operating cost would more than offset any initial savings you saw from its purchase price.