The efficiency figures are Uniform Energy Factors (UEF), the rating on the yellow EnergyGuide label. A typical new electric tank rates about 0.93, a standard gas tank about 0.6 to 0.7, and heat pump water heaters about 3 to 4. Use the numbers from the label of the models you’re comparing for a closer answer.
Gas prices are in dollars per therm; your gas bill lists the rate. If your bill shows CCF (hundred cubic feet), one CCF is close to one therm.