You can get a new garden for free by organizing a seed/plant swap. If you don't have interested friends or neighbors, you can contact churches, schools, Girl Scouts, Boy Scouts and other organizations. Also, local garden clubs may have seed and plant swaps in the spring that you can join.
When I get the urge to start a new flower bed or fill in the bare spots, I first check what I have in stock — this goes for inside and outside plants. Perennials and spring and summer bulbs can easily be divided; daffodils, crocuses and day lilies are fast multipliers. Rooted cuttings and saved seeds also are great to trade. This way, I usually get new varieties to add to my collection at home.
Herbs such as sage, thyme and chives can be dug up and overwintered indoors. Divide them in spring, keep some and swap the others. Houseplant cuttings are always in demand. Unusual plants are more desirable and make better bargaining tools. Don't forget to include compost in your bartering endeavors. Many gardeners don't have room or take time to make compost. I have found that a bag or two of good compost can be worth its weight in free plants!