Driving cross-country or across town has never been easier. Once rare luxury items, navigational systems that use the Global Positioning System, or GPS, are increasingly affordable. But do your homework before buying.

A GPS unit displays maps and step-by-step driving instructions, so you don't have to fight with a foldable map. As long as you're on roads in its map database, it always knows your exact location, so you're never lost. If you make a wrong turn, you'll know precisely how to correct it as long as it has the roads in its database. The companies that provide the mapping software used in GPS units send teams out on the road to keep abreast of new roads and other roadway changes.

Caught in a traffic jam? Some models will suggest an alternate route. And some models incorporate up-to-the-minute traffic data that can help you avoid slowdowns from accidents or road closures. Traffic help sometimes means buying additional equipment or paying to subscribe to a traffic update service, however.

You can pay as little as $100 or more than $1,500 for a portable GPS device. You'll find offerings from Garmin, Lowrance, Magellan, Navman and TomTom.

This is one gadget you'll want to try at a store so that you don't get stuck with a model that is difficult to operate. Lately, GPS manufacturers have added extra features, such as the ability to play MP3, video and picture files. Don't get snagged by the bells and whistles. Here are some features worth considering: