I'll use my wife as an example. She works in an office, 5 days a week. According to Google Maps, her route is 17 miles each way, so 34 miles a day. Taking out weekends, holidays, vacation days, etc, we'll assume that's 225 work days a year.
That's already 7.6k miles. I think it's quite easy, given errands and other things she drives to, to extend and say she's probably driving 10k/year. I think it's actually higher than that, but we'll go with $10K.
Her car is a Lexus RX350. According to the current Lexus site, the RX starts at $50K. The RZ (comparable electric) starts at just under $60K. Without building them out to know all the option packages, that's just under a $10K difference. But with the $7500 tax rebate, that's actually going to be $53K, or a $3K difference for comparable vehicles.
So let's say it's an extra $1500 to install the L2 charger in the garage. Now we're at $4.5K.
Right now gas is around $4.50/gal at the Costco here. SoCal Edison has time-of-use rate plans that averaging winter and summer cost is $0.24/kWh overnight. Both are expensive relative to the rest of the country, but hey, it's California.
Based on
this calculator, the 5 year savings on fuel cost alone will be a little over $5K. So anything beyond about 4.5 years of ownership is saving money based purely on fuel/electricity costs.
And that's not counting potential savings on things like maintenance costs, etc.