Okay, the Toyota Prius costs around $25K and gets around 45mpg in real-world driving on California freeways. The Toyota Yaris costs around $15K and gets around 35mpg in real-world driving on California freeways. So how many hundreds of thousands of miles at $4 per gallon would you have to drive the Prius in order to make that $10K worthwhile? What price would gasoline have to be to make a Prius more cost-effective than a Yaris over the typical 150,000 mile timespan that most people have a car?
First of all: let's look at the fundamental equation. C=G*M/E+P That is, total costs is number of miles divided by mpg, multiplied times the cost per gallon, plus the purchase cost.
So for the first question at 4mpg, we can model it as a 2x2 linear equation and for simplicity set the purchase cost at 10k for the Prius and 0 for the Yaris.
C1=C2 at: 4*m/45+10000=4*m/35... 10000=4*m/35-4*m/45... 2500=m/35-m/45... 2500=45m/1575-35m/1575 ... 2500=10m/1575 ... 3937500 = 10m ... 393750 = m.
So, working the math, at $4 per gallon you would have to drive the Prius for 393,750 miles over the course of its lifetime to make up the $10K cost difference over a Yaris.
So now let's find out what the cost of gas would need to be in order to make the Prius pay off at 150,000 miles:
C1=C2 at: G*150000/45+10000=G*150000/35 ... G*150000/35 - G*1500000/45 = 10000 ... 45 * G * 150000 / 1575 - 35 * G * 150000 / 1575 = 10000 ... 10 * G * 150000 / 1575 = 10000 ... 10 * 150000 * G = 15750000 ... G = $10.50.
In other words, gasoline would need to sell for $10.50 per gallon to make the Prius pay off over the Yaris over the typical 150K miles that most people keep a new car after buying it.
The Prius has some slight advantages over the Yaris. It's roomier, and much quieter inside under typical city driving conditions. On the other hand it also has some significant disadvantages. I'm fairly tall for a penguin, so I get a good view of the top of the windshield bezel if I have the seat fairly upright so I can see well around me (darn those beady little penguin eyes!). The performance is absolutely awful in mountains, once you exhaust the batteries while heading uphill you're basically limited to 45mph or slower. The handling is reminiscent of an old Volkswagen Beetle, in that the weight of all those batteries in the ass end make it want to trade places with the front end and the skinny tires have all the traction of black ice. All in all, once you get pass the gee-whiz factor, there just isn't any compelling reason for a single penguin (who doesn't care about the back seat kneeroom) to buy a Toyota Prius rather than one of the small 3 or 5 door hatchbacks now available for $10K less on the U.S. market. Assuming that the numbers on the cost sheet are similar to the amount of energy needed to create the vehicle, even the environmental argument doesn't work -- if it cost $10K more in energy to build the freepin' thingy at current energy prices, you'll be over 400,000 miles before you'll recapture that energy due to lower fuel use, and who the hell keeps a car for that long anyhow? It'll be at the crushers long before then... well, except the battery pack, which will be at a toxic waste dump (huh!).
-- Badtux the Numbers Penguin