(MONEY Magazine) – Auto manufacturers aren't the only ones in the car business confronting the problems of a still sluggish economy and overstocked lots. So are car-rental firms. Because of an aggressive $45 billion buying program over the past three years, there are 1.1 million cars in the rental fleet now -- nearly 26% more than in 1988. But rental demand is up only 12%. ''There are too many cars chasing too few people,'' reports Charlie Finnie, an industry analyst with Volpe Welty & Co., a San Francisco investment firm. The result: a smorgasbord of special packages that can save travelers as much as 20% or more on weekly rentals. Other deals eliminate those $10 to $200 drop-off fees for renting your car at one location and returning it to another. Still others sweeten rentals with discount coupons. Among today's deals: -- On weekly rentals this year, most firms -- including Avis, Hertz, Budget, National and Dollar, which together control more than 50% of the nation's $10 billion rental market -- have tossed in unlimited free mileage on all models. That means you can avoid excess mileage charges that run as high as 30 cents a mile. -- In the Florida market -- the nation's largest, with the Orlando and Miami airports alone accounting for $100 million in revenue -- the competition is especially intense. Hertz (800-654-3131), for example, is offering a $419 ''Passport'' promotion that includes a week's rental of a full-size car (Ford Taurus or Mercury Sable) plus passes for a family of four to such Orlando attractions as Universal Studios and Sea World. The 12 passes alone can add up to a value of $331 or more. -- In Florida, Hawaii and California, Alamo (800-327-9633) offers discount- coupon books -- good through December -- along with rentals. You can use the coupons, worth $500 to $1,000, at selected restaurants and at attractions like Busch Gardens in Tampa or for, say, balloon rides in the Napa Valley. -- No matter where you rent, Avis (800-331-1212) has eliminated its drop-off fees, meaning you can pick up a car in one city and leave it in another at no extra cost. When renting, remember: -- Book special rates the moment you see them advertised. Car-rental companies have begun to use the computerized yield-management techniques perfected by the airlines. Computer software enables firms to instantaneously tailor price to fluctuating demand. Prompt action gives you a better shot at limited offers. -- Travel over a weekend. Off-peak weekend rates can save you 30% in most cities. Hertz, for instance, now offers promotions as low as $19 a day for subcompacts -- Ford Escort or Toyota Tercel -- if you keep the car over a Saturday night. -- Don't overlook the little guys. Feisty competitors like Alamo, Thrifty and General are sometimes 10% to 20% cheaper than Hertz or Avis. The drawback is that these firms are often located several miles from the airport. Small, independent companies, found in local Yellow Pages, also provide good deals and services, though they lack drop-off facilities. -- Plan flight arrivals and departures for the same time of day. That way you avoid hourly overtime charges that can quickly climb as high as your day rate. -- Beware of added insurance fees. Commonly called the collision damage - waiver, this $8- to $14-a-day option is banned in New York and Illinois altogether. Chances are good that your own auto policy already covers you on rentals. Many credit cards also carry some collision coverage when you charge rental bills. Best advice: know the terms of your policies before you accept or decline the coverage.