Miles per Gallon: 45 Price per Gallon: $3.00 Cost Per Gasoline Mile: 6.67¢ Miles per KWH: 4 Price per KWH: $0.324 (no joke!) Cost Per Electric Mile: 8.10¢
A Tesla is about 0.5 KWH/mile so at the same electricity cost it's far more expensive than a gasoline powered vehicle.
The problem is the high electricity cost in my area. In areas of the country where the electricity cost is half the price then it'd be break-even for the Tesla, and a savings on the Prius. We are not big electricity users since A/C is rarely needed here, and the water heater, furnace, and clothes dryer are natural gas. But we always end up in the top tier for electricity usage ($0.32445/KWH) which starts at 201% over baseline.
The tremendous advantage of a plug-in hybrid, or all-electric, in California, is the carpool lane access with a single person. And due to state and federal tax credits, and factory to buyer incentives, the Prius Plug-In was the same price as the gasoline-only model, and Plug-In came with navigation and several other features. The carpool lane access is really nice even though I don't really agree with the idea that single occupancy vehicles should ever get to use the carpool lane; OTOH, every additional vehicle in the carpool lane means less vehicles in the other lanes so there is some benefit to everyone.