(MONEY Magazine) – Maybe it hit you this summer vacation, grinding your way through tourist-clogged traffic, utterly lost, a little voice from the backseat asking, "Are we there yet?" Wouldn't it be nice, you may have thought, to see your route on a full-color map and be guided through each turn by a gentle, always patient voice (so unlike the one from the passenger seat saying through clenched teeth, "I can't believe you're lost again")? Maybe it was then you decided your next car would have GPS navigation.

But why wait for a new car? In the past couple of years, competent new à la carte systems have lowered the cost of a perfect sense of direction to between $250 and $1,500. That's considerably less than the price of factory-installed versions (it's a $1,900 option on the 2005 Chrysler 300c, for example)—and a whole lot less than a new car.

These new systems vary in the quality of their visuals and sound and, most of all, in their ease of use. But all are built around the same three elements: a Global Positioning System receiver, a color screen positioned in the driver's field of vision and a speaker for turn-by-turn instructions. The GPS receiver picks up radio signals from satellites, then finds your location on a map and plots your route. Most systems also let you browse points of interest like hotels, gas stations or hospitals.

The handhelds

The cheapest GPS devices work with handheld PDAs and consist of a hockey-puck-size module that attaches to your dashboard or windshield plus software that you load into a PDA. A receiver in the puck picks up coordinates from the satellites and relays them to the handheld. Good set-ups also come with suction-cup mounts to hold the PDA in your line of sight, and a power adapter.

Currently the two best PDA products are built around software from TomTom and Navteq. TomTom offers a number of kits for handhelds running either Pocket PC or Palm operating systems, including palmOne's GPS Navigator with Bluetooth ($300) for Palm OS. Navteq powers Dell's new GPS Navigation System ($250) for Bluetooth-capable Pocket PCs. You set them up on a PC (none exist yet for Macs) and then upload the software to your handheld. Both offer colorful interfaces—surprisingly easy to use and read—that rival more expensive navigation kits.

If you don't already own a handheld, you'll want to buy one that has a large screen and Bluetooth capabilities. High-end models of the Dell Axim X30 ($350) and palmOne Tungsten T3 ($400) fit the bill; they would easily raise your total cost, with software, to $600 or so.

Since most handhelds are designed primarily to be address books and planners, they make some compromises as navigators. The screens tend to be small and the built-in speakers weak. Also, if you want to take a long trip, you'll have to buy enough memory to store the relevant maps. Still, there's a lot to say for having all your vital info, including driving directions, on one portable device.

The all-in-ones

If you don't mind carrying a separate piece of hardware to handle your navigation, consider a self-contained system. They are single units that contain receiver, screen, map data and speaker. As with handhelds, portability is a big advantage: Instead of paying $2,000 a pop to build navigation into all your cars, you can buy one unit and share it.

All-in-ones cost as little as $600, but the category's sweet spot is between $1,000 and $1,500. Devices like the Magellan RoadMate 700 ($1,300), the Garmin StreetPilot 2620 ($1,300) and the Cobra's new Nav One 3000 ($1,300) come with maps of the 48 contiguous states plus parts of Canada. All three work out of the box: There's no need to upload software or upgrade a memory card if you plan to travel far. The best of the bunch is the Magellan, which is essentially the same as the NeverLost system in Hertz rental cars.

The built-ins

If you want a system that looks like it came with your car, you can spring for a built-in aftermarket system. Installation costs make this the most expensive way to bring a digital guide onboard. But integrating a system into the vehicle links the GPS with speed and other data from the car, so you get highly accurate location-finding even when the satellite reception is spotty, as it often is in cities and wooded areas.

The additional cost isn't as significant if you're already planning to upgrade your car's entertainment electronics. Pioneer's AVIC-N1 ($2,200 plus installation) mounts in the dashboard with a retractable 6.5-inch touchscreen and, with an extra LCD screen for the rear seats, can double as a DVD player. Another major player is Alpine, supplier to Honda and Acura, where its installations have consistently won high rankings in J.D. Power & Associates surveys. The trunk-mounted Power Nav NVE-N852A ($1,700 plus installation) can be matched up with a monitor or one of Alpine's dashboard Mobile Multimedia Stations, like the DVD-playing IVA-D300 ($1,500).

Whichever system you select, riding with a talking box on your dash will feel at first like having another passenger onboard—usually one with the voice of an accentless American female. But there are other options. When testing the Garmin StreetPilot 2620, for example, my girlfriend and I chose a female voice with a proper BBC accent. Although the system also offered male voices, we passed, as do most users. Maybe we're all afraid that if the male version got lost, it would refuse to ask for directions.

Which type of GPS system is right for you? Plus: The best choices in each category

NOTE: [1]Not including handheld.