You can't afford a Tesla, but can afford a Mercedes Benz and considered a BMW? - huh.
Edit: i'm wrong. See below.
Edit 2: In quite a few places, you can get time of day metering, where you pay lower rates for electricity at night.
In Chicago, I pay $0.01/kwh between midnight and 5am; its essentially free to charge my Model S (it's slightly more at my place in Tampa, ~$0.06/kwh at all hours).