If you like indoor growing, there are simple ways to start tropical plants for free.

Look to your kitchen for a source of free tropical seeds. Save the seeds from fruit, and allow them to dry on a plastic lid.

Citrus Trees - Lemon, Orange, Lime, and Grapefruit - The easiest way to start these is to poke the seeds down about 1/4 inch into the soil of a large houseplant. These will sprout in about ten days, and when the plants are six inches tall, transplant them to individual pots.. Keep the plants in a sunny, warm location, and water well.

Avocado Trees - Forget any complicated sprouting methods. During the summer, bury the seeds pointy end down about two inches under the soil in an outdoor flower bed. This will give the trees a good start on growth, and they won't be tall and sparse like trees started inside. Before the first frost, pot the trees in large pots, and take them indoors. Keep in a sunny, warm spot.

Pineapple Plants - Cut the plant one inch from the leafy top, and allow it to dry for a week on a sunny windowsill. Plant the top in moist potting soil, and keep it well watered. The outer leaves will dry at first, but the plant will shortly begin producing new inner leaves. This plant will eventually produce a pineapple.

Ginger Plants- You can buy small ginger roots for just a few cents at any produece department. Keep the roots until they begin to sprout. Plant in a pot or directly outside in the summer. Cover with just an inch of soil, with the tip os the sprout sticking out of the soil. This produces a big, lush plant in no time at all.

Other Plants : Kiwis, bananas, pomegranate, papaya,and coffee plants are some other possibilities.

Here are some links on growing plants from kitchen seeds:

Growing Avocados from Seed

Raid the Refrigerator: Lemon, Lime, Grapefruit, Orange, Pomegranate, and Papayas

Grow Your Own Ginger

Indoor Pineapple Plant

Coffee Tree - A Unique House Plant

How to Grow a Coffee Tree