Per mile is going to be pretty irritating and people won't like that method. But there should be tax paid, and at the moment, I think it's just under half of the states in the U.S. who have already been doing this for several years. It's just a fixed amount fee that gets paid with the annual registration. The amounts are all over the board, as congress people who don't know #^%$ about electric cars picked them, and depending on how much animosity or support there is for clean vehicles there is in that state determines whether the fee amount is punitive or reasonable. When my electric car hating state first did it, it was $400 per year! I figured up the equivalent gas tax from our Honda Civic Hybrid, and that amount was way more than my real gas tax was.
Some states are going too low I think, with $40 or $50. It should probably be in the mid to upper 100's, maybe near $200.