During our last overseas PCS, our family shipped our huge peoplemover with the intention of purchasing an older car when we arrived. Last time we did this, we went for the $1000 second car. It was cheap and reliable, but I was uncomfortable using it for long distances. As a result, we had to take the jumbo-car and it's 17 mpg even when only a few people were travelling.
This time, I thought it would be more economical to buy a $3000-$4000 second car that would be safe and reliable for trips that didn't need six seats. I fell into a Toyota Prius and bought it sight unseen. I am so glad that I did!
The first month that I owned the car, I drove it over 2000 miles, mostly courtesy of a trip across a large chunk of Europe. The Prius' 50+ mpg meant that I used about 40 gallons of fuel, instead of the 120 gallons that the trip would have consumed in the SUV. Even assuming I was paying US prices, which I was not always able to do, I saved about $320 in fuel the first month alone. And the savings have kept coming. I typically drive at least 1000 miles on my car each month, so I am easily saving $160 a month in fuel. When we are able to take the smaller car on trips, we save even more.
Decreasing our fuel bill has been amazing for our overall budget. As a result, I intend to continue buying high mileage vehicles in the future. I'm not necessarily tied to the hybrid model, though I do love seeing my excess energy being stored and used. There are plenty of non-hybrid options that get excellent gas mileage.
Unfortunately, I don't anticipate the cost of gasoline or diesel fuel going down dramatically in the future. The best we can do to control costs is decrease our driving and use efficient vehicles. It is certain working for me.