It may sound hard, but the reality is that it's quite easy to get into. You need very little effort and stability to do most beginner poses. Because while it's true that modern Yoga has the capacity to push and stretch the limits of the human mind and body, it's also designed to be practiced by all kinds of people, whatever your current physical shape may be.
While strenuous, Yoga is low impact; very little damage is being done to the muscles that are being used. The body's own weight is enough to develop the different areas that are being targeted by each unique pose. When applying proper breathing, the beginner student can easily get in touch with the actual limits of his or her body, and can then eventually stretch those limits through steady practice.
Mentally, the effect is similar to mastering any physically demanding sport or elite activity. Focus is attained through executing poses and breathing. And through focused and disciplined execution, the mind is emptied and refreshed. The student finds progress in his work and becomes content.
Yoga is a real stress killer; not just physically, but mentally. It's a great way to flush out a cluttered mind after a week of hard office work. And if you can't afford weekly classes on a regular basis, simply go to a couple classes and take home everything that you learn. All you need is a bit of room, a non-sliding mat, a large mirror, and the Internet, and you'll be able to research and attempt all the Yoga positions that you want at home.
Just remember to pace yourself. Yoga is a healthy and calming activity. But like any sport, it can get dangerous. So before attempting new and potentially dangerous poses, remember your own body's limits. And, like my Yoga teacher has never failed to remind me, always breathe through your nose.