http://www.teslamotors.com/charging#/calculator. 25,000 miles a year is 68 miles a day which is $2.68 a day, $80.40 a month. It would actually be less as the supercharger trips would be free. That is far less monthly than your Prius costs in gas. That is using sd&e super off peak rate of $0.14/kwh. http://www.sdge.com/ev-rates-resources
The Tesla site calculator does not take into account the cost of adding the second meter, which according to many people on this site, runs around $2K. It also doesn't take into account the 20% ineffeciency loss.
So, I still think the 85kwh model will add about $150 to my electricity bill, which is already $500+ per month.
It doesn't look like it makes financial sense, but cars never do anyway... The intangible experience of driving a fun car def is worth something. The question is, how much?