I had this same reaction when I heard about expensive yoga retreats taught by self-realized yogis.
Now I'm very comfortable with the (often very high) prices that are charged. I've gone to several programs that were over $1,000.
First, every non-profit needs funding. You would not have heard about a particular yoga program if the organization didn't have basic resources to get the word out.
Second, I have noticed that some of the yoga organizations based in India will charge much higher rates in the US and other countries to subsidize either the cheap or free programs in India. This is a great way to "fund" these organizations.
There are many yoga classes out there that cost money; some can be quite expensive. Through my experience with yoga, I've realized the best way to experience it is in my own hands. Yoga classes are good but to find enlightenment within yourself there are other alternatives like apps for the iPhone. Some are Yoga Stretch, Yoga Easy, and Yoga at Home-these are all good yoga apps that explain yoga and even teach you how to breathe properly.