Would eliminating your monthly car payment and other related costs -- insurance, gasoline, maintenance and repairs -- make a difference in meeting your budget?

Maybe you should consider sharing rather than owning a car.

More than 300,000 drivers already have joined more than two dozen car-share programs across the country. They allow drivers to use -- and pay -- for a car only when they need it.

It's possible to save $300 to $500 a month, depending on the cost of the vehicle you're giving up and how often you take to the road in a shared car.

Car sharing makes the most sense if you:

• Live in a city.
• Have access to reliable public transportation.
• Don't need a car every day for work.
• Are at least 21 years old.
• Have a relatively clean driving record.

You can find car-share programs where you would expect: in urban areas like New York City, Chicago and Los Angeles.

But they also turn up in less obvious places: Waterville, Maine; Nashville, Tenn., and Winona, Minn.

Fuel-efficient compact cars comprise the bulk of share fleets, but some larger programs offer pickup trucks, crossovers and midsize cars.

Rental rates vary, but most let members rent by the hour or the day.

Hourly rates range from $3.50 to $13, while daily rates go from $50 to $115.

Operational costs such as parking, gas and insurance are often included.

Other costs may include a small, one-time application fee and annual membership dues or a minimum monthly charge.

Many programs offer business as well as personal and family memberships.

How much can you save?

Let's say you were going to buy a 2009 Honda Civic EX four-door, which will cost $30,018 to own over the next five years, using Edmunds.com's "True Cost to Own" calculator.

That's $500 a month for a relatively frugal model that depreciates at a lower-than-average rate and gets better-than-average fuel economy.

Zipcar is the biggest car-share program with operations in 50 cities. Here's what it costs to use a car for four full days a month with its "Extra Value Plan" in Atlanta:

• A $50 minimum monthly commitment fee, which is applied against the first $50 in rental charges.
• A daily rental charge of $62.90.
• A 45-cent charge for each mile over 180 miles on any single rental.

That works out to $202 a month if you don't incur any extra mileage charges -- or $298 less than it costs to own the Honda Civic EX.

The savings are even bigger when compared to the cost of owning a bigger, more expensive car or truck. Owning a 2009 Ford Taurus SEL, for example, would cost $469 per month more than car sharing.

The tradeoff is obvious. Your ride isn't waiting right outside the back door.

But car-share programs park vehicles in convenient locations around participating cities that can be reserved months in advance or picked up with just a few minutes' notice.

Most programs post an easy-to-navigate area map on their Web sites pinpointing each reserved parking space around the city and identifying the vehicle parked there.

Typically, each program member has a coded identifier of some type -- a card or key fob -- that provides access to any vehicle in the fleet.

After using the vehicle for the prespecified amount of time, the member returns it to the same reserved parking space and walks away.

Car sharing can be a low-cost alternative for car ownership for college students as well.

It's available on more than 60 college campuses.

Student car-share members save money, retain mobility and avoid the hassle of campus parking.

Drivers younger than 21 must have pristine driving records, and their insurance coverage may be more restrictive. But otherwise, membership benefits and responsibilities are about the same.

Carsharing.net has a fairly comprehensive list of the cities served by the various car-share programs.

Getting rid of your car might not be the first choice in a strategy to reduce your monthly fixed expenses.

But if you can live without a vehicle and no other options are open to you, ridding yourself of that expense could put hundreds of extra dollars in your pocket every month.

By Russ Heaps

Interest.com Contributing Editor