If your time is limited and you want to explore the islands in depth, renting a car is the best option. Several international and local rental companies operate on both islands. Expect to pay from around 35 USD per day for a small car, with higher rates during peak season and for larger vehicles. Weekly rates start around 225 USD. Check whether CDW (collision damage waiver) is included.
Drivers must be at least 25 to rent in Trinidad and Tobago. Renting in Tobago is usually a bit pricier than in Trinidad. Rental cars carry R number plates, so they are easily identifiable.