Some of the responses at http://www.mynissanleaf.com/viewtopic.php?f=31&t=7071" onclick="window.open(this.href);return false; might help.
I have no idea if you're going to try to charge at 120 volts or use an L2 EVSE to charge at 240 volts and what its amperage is. Let's assume you do 120 volts and you need to add 19 kWh to the battery (Leaf has ~21 kWh usable battery, out of 24 kWh). You'd need to pull ~25.3 kWh/day from the wall due to the high charging losses at 120 volts.
I can only guess you're on the E-1 schedule (http://www.pge.com/tariffs/tm2/pdf/ELEC_SCHEDS_E-1.pdf" onclick="window.open(this.href);return false
. Since you've told us nothing about what tier you're hitting now, I'm going to assume you're in or near tier 4 already of 33.504 cents/kWh. 25.3 * 0.33504 = $8.48. Even, if you're not, I can only guess charging an EV that much will push you into tier 4.
If you're going to use 120 volts to charge, you will probably have trouble replenishing enough charge each night due to the slowness of 120 volts. 120 volts * 12 amps = 1440 watts = 1.44 kW, so each hour 1.44 kWh comes out of the wall. 25.3 / 1.44 = 17.569 hours, assuming full power the whole time. There is a tapering near the end, but let's count that out for now.
This $8.48 is about the worst case sticking w/E-1 and again, 120 volt charging will not work for you as you progress through the week, unless you switch to L2 charging, have some charging somewhere else (e.g. destinations) or use another car.
Switching to L2 (208/240 volts) even with a 15 or 16 amp L2 EVSE will enable you to fully replenish overnight AND will save you $ on electricity costs, as the charging losses are lower.
Again, if your drives are mostly highway and you own the the car, the commute will get dicey in winter, as the battery degrades. You will have to slow down and/or limit heat usage...and eventually, you won't make it unless you slow way down or charge in between/at destination.
BTW, I had to kinda guess about "tiered base plan" as people don't normally use that terminology. I found http://www.pge.com/en/myhome/saveenergymoney/plans/tiers/index.page" onclick="window.open(this.href);return false;. I'm on E-6 Smart (soon to switch to just E-6). I was on E-1.
I think you should try http://www.pge.com/cgi-bin/pevcalculator/PEV" onclick="window.open(this.href);return false;.