In reply to Indy:
like everything Indy, yoga can be subject to greed
As for how many classes one needs to become 'proficient' enough, that is impossible to answer I'm afraid. There really is no such thing as the average person in my experience.
But, and I'm sure you don't really want to hear this, we are probably talking more in terms of years than classes.
If you're really interested in yoga, then i suggest finding a good local yoga centre and trying out some classes until you find a teacher you click with...then going to see them at least twice a week and see how it goes.
Gym yoga, in my experience, is generally not the best standard, though of course there may be exceptions.
If you fancy a few months in the sun, then come to the Dominican Republic where i teach....a month of classes for 40 quid!
ps private tuition tends to be super-pricey and largely unnecessary in my opinion
Post edited at 11:58