Here's some information on car rentals in Belize, from my latest book, Belize First Guide to Mainland Belize.
I suspect you'd get the best rate by dealing directly with car renters, as that way they don't have to pay a travel agent commission. I don't know of any package plans that include a car, though there may be some.
For what it's worth, my favorite car rental company in Belize is Budget, though several others are very good, too, including Crystal, Hertz and Thrifty.
Belize First Magazine http://www.turq.com/belizefirst/
Car: Many first-time travelers to Belize are reluctant to rent a car. They’ve heard that car rentals are expensive and roads are terrible. Auto rentals in Belize are more costly than in most of the U.S. (though generally less than in Europe or Asia), and some roads are bad, especially in rainy weather. (See the Driving in Belize section for complete information on all Belize roads and driving conditions.) Overall, though, on mainland trips you’re likely to save money if you have your own wheels, and that’s doubly true if you’re traveling with several other people. With a car, you can avoid paying high tour fees for destinations you can easily visit on your own, such as the Belize Zoo, Crooked Tree, the Baboon Sanctuary and most Maya sites. You can also set your own schedule, stopping and going exactly when you want to.
Roads in Belize are increasingly well marked, and except in Belize City with its confusing jumble of one-way streets, or at night, you’ll rarely get lost. Three of Belize’s four main highways are in excellent shape. The Northern Highway, Western Highway and Hummingbird Highway are black-topped two-lane roads. The Southern Highway is being paved, but there still are long stretches south of Independence and north of Big Falls that are not in good shape.
The focus of car rental in Belize is the international airport, where about 10 rental agencies have booths. Just walk out the main airport exit from the lobby, cross the street, and the car rental offices are a few yards away at the far side of the airport parking lot.
TIP: Many of the car rental booths are closed on Sundays, so if you’re arriving on Sunday make prior arrangements to have an agent meet you. Most of these car rental companies also have locations in the city.
Among recommended auto rental firms are: Budget (international airport and 771 Bella Vista, Northern Hwy., tel. 501-2-32435, fax 2-30237, or in the U.S. and Canada tel. 800-527-0700, e-mail firstname.lastname@example.org, www.budget-belize.com);
Crystal (international airport and Mile 1 1/2 Northern Hwy., tel. 501-2-31600, fax 2-31900 or 800-279-7825, e-mail email@example.com, www.crystalbelize.com);
Hertz (international airport and 11A Cork St. next to the Radisson Fort George, tel. 501-2-35395 or in the U.S. and Canada tel. 800-654-3131; e-mail firstname.lastname@example.org; and Thrifty (corner Central American Blvd. and Fabers Rd., tel. 501-2-71271, fax 2-71421 or in the U.S. and Canada tel. 800-367-2277, e-mail email@example.com.)
TIP: The operator of the Budget franchise in Belize, JMA Motors, also owns the Suzuki and Mitsubishi new car dealerships, so Budget vehicles tend to be well-maintained and with lower mileage than most. We’ve found Budget to be, overall, the best auto rental company in Belize.
Some typical prices for rentals:
Geo Tracker 4x4 convertible, from Crystal: US$78.95 per day or US$449 a week; Nissan Pathfinder 4x4 SUV, from Crystal: US$98.95 per day or US$599 a week; Suzuki Jimny 4x4, from Budget: US$75 a day high-season, US$70 off-season, or US$450 a week high-season, US$420 off-season; Mitsubishi 12-person van, from Budget: US$100 a day high-season, US$95 off-season, or US$600 a week high-season, US$570 off-season. Rates are unlimited mileage and do not include 8% sales tax or Collision Damage Waiver insurance.
Cars rented in Belize have liability insurance included in the rate, but not collision, and auto rental firms usually try to sell you CDW, at US$10 to $15 a day, to cover damage to the car from an accident, burglary, broken windshields or similar. Even with the CDW insurance, you may be liable for the first US$500 to $1,000 or more of damage. We call this a rip-off.
TIP: Some credit cards cover CDW in Belize. Call to see if yours does and save yourself up to US$90 or more a week in CDW costs. However, be sure it covers four-wheel drive vehicles and driving on unpaved roads. We have had good luck with American Express’ CDW coverage. Belize does not have an AAA or other auto club, so your club membership will do you no good in Belize.