Often it's cheaper to buy your food in supermarkets than to grow it. To get into gardening, you need reasons other than "To save money." Consider these:
It's a great way to learn about Nature. The garden is a kind of ecosystem with its own energy flow, and nutrient recycle. Watching wasps collect spiders from your squash plants teaches more about predator/prey relationships than reading a whole chapter on it. Soil has its own ecology and if you don't understand it your plants may die. If you don't learn that pretty cabbage moths leave behind eggs from which caterpillars emerge to eat your cabbage, you may lose your cabbage crop. Every garden is a zoo and a botanical garden with thousands of different kinds of organisms interacting in complex, often mutually beneficial and always interesting ways. All the basic patterns of Nature exist in any average garden.
Freshly picked food is healthier to eat and tastes better than store-bought, processed food. Store-bought vegetables normally have been picked before they were mature, so they wouldn't bruise as badly when shipped. Chemicals may be used to cause them to ripen when it's time to display them. Also, the longer the period between a vegetable's harvest and when it's eaten, the more nutrients are lost. Moreover, just look at all the chemical additives added to your store-bought foods to preserve them, color them and add taste. Fresh food grown by you and not contaminated by chemicals is much better for you and tastes better than average store-bought food.
Working in the garden is healthy for you. With all its stooping, digging, hoeing, carrying, etc. it provides exercise you may not get in your everyday life. It not only burns calories and strengthens the heart and hands, but also reduces stress. Simply exposing oneself to sunlight increases vitamin D in the body, which enhances calcium levels, especially important for women and older adults. However, for most of us, maybe the main benefits are psychological. Planting, tilling, nurturing and harvesting plants builds self-esteem and "roots" us in the Earth. Gardening reduces stress and symptoms of depression and anxiety. In the end, gardening simply makes us happy.
In a monotonous, routine-filled world, gardening can be a very pleasing aesthetic experience. Moreover, it's an experience you can share with others.
Gardening helps heal the Earth. Sometimes it seems that everything we do ends up killing something nice or destroying a part of Nature we don't mean to hurt. Gardening gives us a chance to help Nature restore herself. The plants we grow convert industry's carbon dioxide to breathable oxygen. Adding organic matter to garden soil improves the soil's structure, benefiting the soil's microflora and -fauna. Gardening increases species diversity on the ground it occupies. When we eat something from our own backyards we're not paying people to transport produce from distant parts of the world, keeping it cool all the time, producing carbon dioxide and other pollutants all along the way.
Gardening is fun and even therapeutic. Each morning you walk out and see how things have grown, what's been nibbled on during the night, what might be harvested that day... You just walk around and it's like visiting an old friend who has changed overnight! Moreover, when you fill your head with thoughts about flowers and fruits, soil, bugs, weeds, tools, fertilizer, etc., those thoughts replace gloomier, negative thoughts. The garden heals the sad, unhappy spirit!
And it CAN reduce your food bill. Most gardens in towns and suburbs are more hobbies than serious efforts to produce food for the daily table. However, if you really grow what you want to eat, preserve those things with canning and freezing, or storing in cool, dry places, and truly prepare and eat your harvests instead of going out or eating processed food, the savings can be substantial.