Also, another affordable way to extend the distance between the sensor and the lens is to use a set of tubes. They come in sets of three and in different lengths which could be 10, 20 and 30mm. This way, you can put on the shortest, or stack all three or any combination in between, giving you a greater variety of lengths. It is not as finely adjustable as the bellows, but they work well. They are also much smaller and easier to handle, and to bring with you in your camera bag.
You can find them very cheap at Amazon. Since they are, in their simplicity, just some aluminium tubes, they come with a nice price tag. Remember to buy those with the mount fitting your camera.
It is a low cost starting point into the world of macro photography.