If most days you run 75% EV and 25% gas, you are ahead of the Prius in mileage.
Not really. The breakdown I did was 100% EV use in the Volt and all gas use in the Prius over 20,000 kms year. In that breakdown, you'd need to use the Volt for 17 years in solid EV mode (no gas
ever) to recoup ANY cost savings over owning a Prius. Based on your 75/25 scenario I get:
Per year:
Gas for Prius = $987
75% EV mode for Volt. Charge for Volt, assuming 80kms per charge (conservative) = $188 (assuming less conservative 60km/charge = $250). 25% gas cost: $294
~$42 per month savings in favor of Volt for fuel/electricity. (or $37 a month less conservative).
We have to see what the Volt lease rate will be over here before we can make an absolute determination of how cheap it will be to run the Volt vs Prius.
But if we factor in the current USA lease rates of $269/month for the Prius, and $350/month for the Volt, it's still cheaper to own the Prius even with the good Volt lease rate.