Yoga is a fabulous practice that can benefit anyone, of any age, and of any ability/mobility. it is excellent for bringing about a strong, healthy body. There are many other links--somewhere on here--related to this topic!
there are also a number of good web sites out there, such as yoga journal, yoga international (himalayan institute), moving into stillness, and a myriad of others.
there are also a number of great books and videos out there for you to try, but i would highly recommend taking classes with a teacher if you can.
don't worry about costs--ask if they give a first class for free or if they are willing to trade work for classes.
many studio's will (including mine!).
Now, there are many styles of yoga. I find kripalu and sivananda to be great for gentle hatha yoga (yoga of asana, or postures) as well as meditation and relaxation. Astanga and power yogas are generally more vigorous, but can also be deeply restorative and ultimately very relaxing. i teach a blend--a more gentle vinyasa for the most part--so that students are balanced and happy.
if you live in the philadelphia area, feel free to come by the studio. my web address is ouryogastudio.com. you can check out what we're up to!
Good luck! be well and happy!