Few hotels provide airport transfers, but you can always ask when you make your reservations. If you've booked a package, sometimes transfers are included. In Trinidad, taxis are readily available at Piarco Airport; the fare to Port of Spain is set at $38 ($58 after 10 PM). In Tobago the fare from Crown Point Airport to Scarborough or Grafton Beach is about $65.
Renting a Car: Don't rent a car if you're staying in Port of Spain, but if you're planning to tour Trinidad, you'll need some wheels, as you will if you end up staying out on the island. In Tobago you're better off renting a four-wheel-drive vehicle than relying on expensive taxi service. Be cautious driving on either island, as the country has very lax and seldom-enforced drinking and driving laws.