There are several options you have. I know of a car rental company which operates in Maiquetia, its name is Budget Car Rental (www.budget.com.ve). There is another company, AVIS (http://www.avis.com.ve), which even gives you the option, in plain English, to reserve your car. Entering the period of time suggested by you in the AVIS online system, you will have to pay around $ 2600.
Some more links for you to check out:
http://www.amigoscarental.com/ (This one has an English version).
http://www.acorentacar.com/ (For a compact, Toyota Yaris you'd be paying around $ 988 per week, at a base rate)
So, in order to rent a car for three weeks you must have between $ 2500 and $ 4500 at your disposal. Obviously, there are some other requisites: you must be older than 25, possess a valid driver's license, and in most cases a credit card.
More companies are spread across Caracas, but these will surely give you an idea of the renting process.
Traffic jams are common within Caracas during most of the day. Driving regulations are similar to those in the U.S. although many drivers do not obey them.
Defensive driving is a necessity. Child car seats and seatbelts are not required and are seldom available in car rentals and taxis.
Outside the major cities, night driving can be dangerous because of unmarked road damage or repairs in progress, unlighted vehicles and livestock.
Even in urban areas, road damage is often marked by a pile of rocks or sticks left by passersby near or in the pothole or crevice, without flares or other devices to highlight the danger.
Stops at National Guard and local police checkpoints (alcabalas) are mandatory. Drivers should follow all National Guard instructions and be prepared to show vehicle and insurance papers and passports.
Vehicles may be searched.
Economical bus service is available to most destinations throughout the country. Peak holiday travel occurs during summer and winter school breaks and major civil and religious holidays, including Carnival, Easter, Christmas and New Years holidays.
Lengthy delays due to road congestion are common during these peak periods
Holy Cow! Caracas has the coolest/craziest driving conditions I have ever had the pleasure of experiencing! Dont confuse my optimism for an endorsement. Driving in Caracas is not for the light hearted. You will find traffic lights/signs in this wonderful city but do not expect to find people adhering to them. Use your offensive driving skills or stay off the road. If you are not prepared to be a rude driver, you will never make it to point B! I suggest you hire a taxi and observe before you try it yourself.
The traffic in Caracas can be annoyance; you can log time because the traffic. Take your precaution if you have to be on time.
And get worse when it rains I will said that the city collapsed, then be patient and be prepared to a long time in the car.