More than half of them are quoting this website -
Pakistan to Acquire 75 F-16 and 150 JF-17 Fighters, which is just another blog on which anyone can write anything on. As per quoted information on Jane defence weekly, The upgrade would involve 50 aircraft, plus another 50 on option, that would go into production in 2013, following delivery of the first batch of Pakistani air force JF-17s. The project could be worth up to 1 billion ($1.36 billion), more than double the $500 million that the JF-17 development reputedly cost. Bhaijan mein apko sahi informatino de raha hoon, aap kud hi check kar lo lol