If you'll soon be in the market for a new car, chances are you care most about the gas mileage it'll get. But what kind of car will really save you the most in gas over the long run? NewsChannel5's John Matarese conducted a monthlong investigation to find out.

What Shoppers Want

Liz Brunner couldn't care less about leather seats these days: All she wants in her new car is fuel efficiency.

Liz said, "I have to travel on the highway for my job, so I definitely need something fuel efficient."

But which of the following three options would save her the most over five years? A hybrid Toyota Prius, with its sticker promising 45 to 48 miles per gallon or a non-hybrid economy car like the Toyota Yaris, which gets 29 to 35 mpg, according to the EPA sticker?

Or what about a Flex Fuel car using E85 ethanol, which sells for about 50 cents less per gallon than gasoline, if you can find it?

Only a few stations offer E85, and almost all are in the Midwest.

NewsChannel5 Tests A Hot Hybrid

To find out which is the best money-saving option, NewsChannel5 drove three vehicles and crunched the numbers, starting with the hot-selling Prius.

At Joseph Toyota of Cincinnati on Colerain Avenue, salesman Nick Weisbord said there's now a waiting list for a Prius, here and at almost every Toyota dealer in the country.

"It's going to take three months at this point," he said.

But we were able to rent a Prius from Enterprise. Producer Sean Dunster then drove it on his daily commute: five days to and from work, on mostly interstate highways, for a total of 265 miles.

His average mileage was 42.1 miles per gallon.

Testing An Economy Car

We then turned to the gas-powered Toyota Yaris, cheaper and a bit easier to find. Weisbord said the Yaris has suddenly become a hot seller, due to its mileage and surprising interior space.

"This came out about a year ago. Sales are very good," he said.

So we rented a Yaris, and Dunster made the exact same one-week commute. His average mileage was 37.9 miles per gallon.

Testing A Flex-Fuel Car

But what about flex-fuel? We found E85 ethanol selling for 50 cents less than gas. That's the one good thing about it. The downsides are that E85 is very hard to find and that the EPA said it will reduce a car's mileage by 15 percent, compared with gasoline.

Meantime, the EPA does not yet list any subcompact flex-fuel cars, so we rented a Chevrolet Impala, one of the smallest flex-fuel vehicles available.

Dunster then drove the Impala for one week, just like the other cars. He averaged 25.6 miles per gallon.

Crunching The Numbers

But what about the total cost? The Prius' base price is $21,550, and don't expect any discount. The Yaris' base is price is just $13,150, significantly less than the Prius. The Impala starts at $22,725.

The initial cost was then added to what you'd pay for fuel over five years, assuming $4 gas and 15,000 miles per year.

The big winner is actually the Yaris because the Yaris' total cost -- car plus fuel -- is roughly $22,000 over five years.

That's far less than the Prius's $28,000 cost or the flex-fuel Impala's $33,000.

The hybrid Prius wins the sheer mileage numbers, but you pay what's called a "hybrid premium" to own one. In fact, all hybrids will cost you several thousand dollars more than similar non-hybrid cars.

In the past, you could receive a tax break, but those have now expired for Toyotas and several other popular hybrids.

If you want to make an environmental statement or simply get the best mileage possible, then the Prius is a great vehicle, and could be for you.

But if total cost is more important to you, a small gas-powered car like the Yaris or others from other automakers might be your best bet.

Methodology: We based our findings on Edmunds.com MSRP base price for each vehicle. As of 7/1/08, Edmunds listed the Prius at $23,770, the Yaris at $13,170 and the Impala at $22,725. Those prices included air conditioning and stereo, but in the Yaris' base price did not include the power window package, which is extra. The Prius typically sells for sticker or higher. The Yaris and Impala often sell below sticker, which would actually favor the Yaris even more in a comparison.

Since it is impossible to predict future fuel costs, we computed fuel costs over five years assuming gas remains at $4, and E85 remains at $3.50.

Based on the above numbers, five-year fuel charges for each vehicle were as follows: The Pruis: $7,125. The Yaris: $7,950. The Impala, on E85: $10,275.

We then added five-year fuel costs to the vehicle price. We did not factor in future trade-in value, as it is impossible to predict values five years in the future. Based on Kelly Blue Book history, however, the Prius would retain the highest trade-in value, while the Impala would lose the most value over five years.

Countering the Prius' trade-in advantage: possible replacement of the Prius' hybrid battery. The length of the battery's warranty varies from state to state, as it is covered by state emissions laws. We did not factor that in.

Using historical trade-in valuations, it does not appear that trade-in value would change the end result of our findings.