(MONEY Magazine) – With prices virtually flat for the past 10 years, rental cars have been the last great travel bargain. But hang on to your steering wheel: Big changes in the industry mean you're going to pay about 30% more than you did a year ago and you'll drive away in an older, more road-weary car. That is, if you can find one. ! Here's what happened: For the past few recessionary years, General Motors, Ford and Chrysler, which hold sizable stakes in the large rental firms, had used rental fleets as dumping grounds for excess inventory. The Detroit automakers gave rental firms $400 to $1,400 rebates per car plus promises to buy back autos after four months. Since 1991, however, such policies have cannibalized new-car sales. So last September, auto manufacturers eliminated rebates for 1993 models. And they extended the rental-car road life by promising to buy back cars in six to nine months, not four. Those vanished rebates helped create a 25% to 35% cost increase for the $11.5 billion industry, says Joseph Russo at Hertz, the 230,000-vehicle industry leader. As a result, Hertz's base rates -- its lowest advertised economy car rates -- have gone up 30% since last year. ''A year or so ago, you could find a small car in Florida for $59 to $69 a week,'' says Travel Weekly's Henry Magenheim. ''Now it's hard to find one for under $100 a week.'' But you can whittle down that steep 30% increase: -- Shop hard for deals. Enlist an experienced travel agent to scan computerized reservation systems for low prices and short-term promotions. Many large firms, notably Alamo (800-327-9633) and Budget (800-527-0700), provide agents with discount coupons good for about 20% off at hotels, free car upgrades and sometimes 10% off rental rates. A dedicated agent can also alert you to high-value fly-drive packages that were locked in last spring before prices rose. For example, American Airlines' Fly AAway Vacations (800-321-2121) to 13 Florida cities include an economy car for $73 a week. Sample package (without air fare): Seven nights at Fort Lauderdale's 250-mini-suite Crown Sterling Suites Hotel, including breakfast and an economy car with unlimited mileage, for $351 per person, double occupancy. Typically, travel agent commissions run 10%, which nets an agent only $10 on a $100 weekly rental fee. So if all you're booking is a car and the agent doesn't get your other business, consider searching for advertised specials yourself. When you do, try to rent over weekends or for full weeks to avoid high daily tariffs. For example: In Denver recently, Avis' weekday rate was $39.99, a weekend day ran $28.99, and a full week cost $134.99. -- Look beyond the Big Four. Together, Avis, Budget, Hertz and National account for 56% of the rental-car market, according to Gary Rubin of Auto Rental News. Smaller national firms, however, such as Agency (800-321-1972), Enterprise (800-325-8007) and Snappy (check local listings), which primarily rent to local owners whose wheels are in the shop, sometimes peg prices at 50% less. Warning: Most of these firms' rental offices are far from airports. -- Join a club. You may qualify for discounts through your employer's corporate account or as a member of a professional, trade or travel group, such as the American Automobile Association. National, for instance, is offering special rates through April 30 to frequent-flier members of Continental, Midwest Express, Northwest, United or USAir. Example: In L.A., a compact car costs $19.95 a day Thursday through Monday. -- Ask for low-mileage cars. ''Cars used to be so new that few renters had problems,'' says Travel Weekly's Magenheim. ''But now you'll find cars with 30,000 miles on them instead of 10,000.'' Odds are cars will get shabbier and more prone to mechanical trouble. Although requesting a low-mileage car is no guarantee you'll get one, it's worth a try. Book in advance to avoid shortages. Fleet sizes may shrink as much as 10% in 1993, so you might not get the car you want. Rental firms insist there will be cars to meet demand, but Thomas Nulty, president of Associated Travel Management in Santa Ana, Calif., reports problems finding cars since October. Make reservations well ahead of time, and write down your confirmation number as proof of booking. -- Be prepared for beefed-up taxes and fees. More airports are imposing taxes of 7% to 10% on customers of off-airport rental firms who arrive via free shuttle bus. Options may go up too, such as fees for extra drivers (now about $3 a day) and drivers under age 25 (about $15). You may not be told about extra charges unless you ask.

And don't fall for the firms' hard-sell tactics for $9- to $13-a-day collision damage waivers (CDWs), which relieve you from financial responsibility if you damage the car. Last November, Budget agreed to pay the State of Hawaii $100,000 to settle a case stemming in part from overzealous sales of CDWs. Your auto insurance policy or charge card -- American Express, Diners Club, MasterCard Gold or Visa Gold -- may provide coverage that makes a CDW unnecessary. Call your insurer or card issuer for details. Perhaps the most notorious surcharge comes from Hertz, which in 1992 began charging New York City residents who rent locally as much as $56 more a day. Hertz, now embroiled in a court battle with the city, says it needs the charge to cover skyrocketing costs of liability lawsuits there. Such fees are therefore unlikely to pop up elsewhere.