Spend about $36.00 in 5 minutes to drive for another 350 miles or about $3.00 in 20 to drive about another 64 miles (assuming comparable subcompacts, highway miles). Keep in mind, you will spend that 5 minutes fueling at a gas station, where you can charge at home and possibly at work, play, and shopping. So, if your idle time is really valuable, or you just go on long trips frequently, you may want to keep a gas car around.
I putter along at about 25 miles per day, with the odd 200 mile trip every few months where I don't mind stopping a couple of times to stretch, take a leak, grab some grub, etc... So, about every quarter, I would drive about 2350 miles. I would spend about 40 minutes during that time fueling my gas car (33 mpg combined, 9 gallons per stop), and 1 hour 20 minutes (4 80% recharges) screwing around at charging stations (20 minutes for 19.2kWh, 80% of a 24kWh pack, 64 miles per). I will have spent about $285 in Gas or about $12 at the charging stations, plus about $94 in household electricity (assuming no "free" charging).
That is about $269 per hour of waiting. Although, this does not include offsets such as the huge upfront cost of the pack (usually a $12k to $14k premium), nor the large difference in maintenance costs. It also does not include the few seconds to plug in the car at home, now that I think about it.