Did Iran Already Buy Soviet Nuclear Weapons?

In autumn 1991 Nursultan Nazarbayev, the president of Khazakhstan, sold three nuclear warheads to the Iranians. The Iranians wanted to use them as a prototype for their own bomb manufacturing. The price was said to have been 7.5 billion USD. Whether this amount is true or just the fantasies of a less paid government official, I cannot verify. The amount was to cover all bribes and kick-offs and military protection during transport. Every country involved had demanded their fair share of the deal.