I've had the opportunity to take and teach yoga all over the world and here's my secret to free or at least discounted classes. Discounted classes: Almost every studio has a huge first week or first month pass for new members. It's usually $20-$25 for the week or $50 for the month. With so many yoga studios in major cities, I'd just go from studio to studio. Or they will have karma/community classes taught by new yoga teachers for either a donation or $6-$8. Free classes: Most studios will offer a first class free. They don't usually advertise it, but you can call up and ask. As well, they'll offer you a free pass if you donate a few hours of your time each week. You work their desk for a 3 hour shift each week and you get free yoga for the rest of the month. If you're not much for desk work, usually there's a cleaning shift available.
If you are going to go from studio to studio, Groupon and/or Living Social is another easy way to save on Yoga classes. I see deals for yoga with enough regularity that it would be easy to fill an entire year with classes (in a big enough city) for very little. To be honest, I'm not a huge fan of studio hopping, because once I find a class or an instructor I like, I really want to stick with the journey that he or she will take me on. I've found the best deal for yoga classes to be through a gym membership that includes a yoga studio. Two of my best yoga instructors of all time worked at the YMCA, and my membership fee (that I'd pay anyway because my family uses the Y for everything) covered all classes.
If you'd like to keep Yoga affordable, and are a good independent exerciser, I would just go straight to YouTube and access hundreds of great workouts. I've never had any problems finding the kinds of workouts I've been looking for, and as long as I keep up with it, it's definitely cheaper and less time-consuming than finding classes to attend. But if classes are what you're seeking, community centers are usually the best resource!
Great timing. I was standing in line to buy groceries and spotted a yoga magazine. The woman on the cover was a pose that can only be done because she has a strong core. That's what I want! I have been thinking about how I could take some yoga classes on the cheap. Great ideas in this thread. I use YouTube for other exercises, but never thought to check out yoga videos.