I tried to emulate the math you showed, my Chevrolet Bolt EV emits 96g CO2 per mile when considering upstream emissions on the New Jersey electrical grid, my carbon tax on 96kg emissions per 1000 miles would be $17.76.
Seems about right. The EPA uses a conversion factor of 8887 g CO2 emitted per gallon of gasoline consumed. [1] Assuming 40 miles per gallon, as above, that's ~222 grams per mile for the theoretical ICE car, a little over 2x the emissions of your electric vehicle.
Incidentally, 2023 Bolt specs [2] indicate an efficiency of about 4 miles per kWh, and the EPA reference above states a typical US grid efficiency of 4.17 × 10^-4 metric tons CO2/kWh. This gives us 15.38 km per kg CO2. So ~105 kg of CO2 would be released by driving a Bolt for 1000 miles on typical grid sources. [3]
I'm surprised to learn the US grid is this inefficient. In theory, an ICE car with an efficiency of 85 mpg would emit less CO2 than an electric car. Obviously that's not reachable at this point, but a hybrid like a Prius that can hit 57 mpg cuts it a lot closer than I would've thought.
Does that sound right to you?