"I'm thinking about getting certified but this rip-off thing is something what is holding me. I do not want to pay bunch of money just to hear again something I've already know or not interested in (like chanting)"
Initially, the yogic sciences have never had any kind of certification, it is not an academic study. It has less to do with gathering knowledge, and more to do with coming to know yourself, through and through, and the transformation that arises out of coming to know oneself. The closest thing to any kind of "ceritfication" has been to be initiated into a tradition, which is itself not really a necessity for awakening. Most of the yogic sciences for centuries were just transmitted orally from master to disciple, there has never been a need to drag something as superficial as certification into the matter. Do you think that Patanjali has any certification, or Gautama Buddha ? A master is always uncertified, because a master does not mean a master over a particular subject, or a field of study. It simply means one who has come to know oneself, who has awakened to his original nature and is in living communion with one's true self. A disciple does not require any certification either, because a disciple just means one who is initiating a discipline.
Since yoga had become imported from the East to the West, it has just become a commodity, a product in the marketplace which is just intended to fulfill the demand and supply of the people in the marketplace. Because the conditioning of the Western mind has been revolving around the ways of the body, now everything in yoga has become just about the body. All those more physical techniques which were intended just as preparation for meditation - have now all been reduced to just a series of physical exercises, or as a way to reduce stress. What was a gateway to the divine has now become just part of the ego-nourishing industry which has spread almost all over the Earth. In this way, what has happened has been a great disservice to the science, it has lost it's original spirit for the sake of man's greed.
Yoga, if one is going to consider it according to the very meaning of the word, Union, does not require certification of any kind. But certainly it requires qualification. And the qualification is, not through degrees, but through coming to a direct experience of your original nature and liberation from the causes of suffering. Only one who has ignited his own flame can become capable of triggering it's discovery in another, only a Buddha is capable of assisting another towards his Buddhahood.
But if what one is calling yoga is the kind of yoga that exists in the market, then it does not require much. Just a few months of a few years of training to receive a certificate is enough - and you can start teaching yoga.