According to a J.D. Power and Associates study, most shoppers buy green cars to combat the rising price of gas, not to decrease their environmental impact. The truth is, not all eco-friendly cars are as kind to your wallet as you might think. We’ve compared four models to help you make the most fuel-efficient and budget-friendly choice.

Hyundai Elantra vs. Chevrolet Cruze ECO

The Hyundai Elantra and the Chevrolet Cruze are two of the largest cars in the small car class. Each has more than 33 inches of leg room in the back seat, compared to 31.2 inches in the Ford Fiesta, and most car reviewers say they look and feel more expensive than their competitors. The Elantra gets 29/40 mpg city/highway, and the Cruze gets up to 28/42 mpg city/highway.

While the Elantra and Cruze sound about equal, there’s a catch. To get that fuel economy in the Cruze, you have to upgrade to the Cruze ECO trim, which starts at $18,425. That’s $1,900 more than the base model with a manual transmission. If you select an automatic transmission, that 28/42 mpg city/highway drops to 26/37 mpg city/highway and tacks on an additional $925, bringing the Cruze ECO to $19,875, which is a lot for an affordable small car with lower fuel economy ratings than the base Ford Fiesta. (The Fiesta gets 29/38 mpg city/highway.)

The Hyundai Elantra, however, has no ECO trim. The basic GLS trim and the top-of-the-line Limited trim both average 29/40 mpg city/highway. That means if you can drive a manual and forego air conditioning, you can pay $14,495 for the Elantra and still get 40 mpg on the highway, saving $3,930 compared to the Cruze ECO with a manual transmission.

But, most shoppers will want an automatic transmission and a few amenities. When the Cruze ECO and the Elantra are similarly equipped, the Elantra still comes out on top. Adding the Popular Equipment Package to the Elantra, which includes air conditioning, cruise control and a telescopic steering wheel, brings the price to $17,195, which is $1,230 less than the Cruze ECO.

Not only will you save $1,230 right off the bat, but you’ll also save over $200 in fuel costs each year with the Elantra. If gasoline is $3.90 a gallon and you average 29/40 mpg city/highway in the Elantra, you’ll pay 13.4 cents for every mile you drive in the city and 9.8 cents for every mile you drive on the highway. Let’s say you drive 8,250 miles in the city and 6,750 miles on the highway each year. After you do the math, the Elantra’s annual fuel costs are $1,760 and the Cruze’s is $1,980. That’s a $220 difference.

The Elantra also has more optional features. Navigation, sunroof, leather seats, premium audio system and heated front seats aren’t available on the Cruze ECO (though you can get them on other Cruze trims – you just won’t get as good fuel economy). Select the Elantra Limited and add the Premium Package, and you get these same features plus heated rear seats, a rear view camera and push-button start for $22,295. With every available feature added (power adjustable front seat, remote vehicle start, cruise control, Bluetooth and leather steering wheel with mounted controls), the Cruze ECO costs $20,560. The Elantra is just $1,735 more and has more features.  If you don’t want all these features, an Elantra with Bluetooth, cruise control and steering wheel mounted controls is less than the ECO at $17,745.

Honda Civic Hybrid vs. Honda Civic HF

If you’re a Honda loyalist and want the 2012 model, you’ll probably take a look at the new Honda Civic High Fuel-Efficiency model, a more fuel-efficient version of the gasoline model, and the Honda Civic Hybrid. The Hybrid seems like the best deal because it gets 44/44 mpg city/highway according to Honda, but its base price of $24,050 is $4,595 more than the Civic HF. In the end, the Hybrid’s high price tag makes the Civic HF the best choice for your wallet, even though its fuel economy is worse at 29/41 mpg city/highway.

With regular gas priced at $3.90 a gallon, you’ll pay 8.9 cents for every mile you drive in the Civic Hybrid. If you drive 15,000 miles a year, your annual fuel costs will be $1,335. Because it has lower ratings, you’ll pay $1,746.75 to gas your Civic HF in one year. That’s a significant yearly savings, but the Hybrid is only worth the price jump if you plan to own it for a long time. It would take about 11 years of driving to make up the $4,595 difference between the Civic Hybrid and HF in gas savings.

Despite these savings, there is one downside to choosing the HF. There’s only one trim available, which means you don’t get features like Bluetooth, navigation, XM Satellite Radio or leather seats, which are available on the Civic Hybrid. Bluetooth is standard on the Hybrid, but adding leather, navigation and XM Satellite Radio brings the price to $26,750. If you want a Civic, good fuel economy, every feature and don’t mind paying about $27,000, the Civic Hybrid is the better option.

No matter which cars you compare, don’t assume that a car that saves on gas will end up saving you money in the long term. The money-saving option may not be the greenest one.