The majority of body builders get their testosterone undecanoate from the black market. In the USA the product is only available on the black market. Generic forms of the steroid have been made in Europe, Japan, Mexico, Spain, Brazil and Thailand. However, in each case the quality and the purity of the product is highly questionable.
Most body builders use between 50-400mg/day and 50 (40 mg) for about $60-$100. However, like all things in cyberspace the purity and quality of the product is always in question. And fakes products are plentiful.