Here is what I have seen for the value before, hopefully someone will update if incorrect.
The sale of Uranium One was for 1.3 Billion.
As that article states, that price was low and due to the falling price of uranium itself, and the company had been valued at 5 billion just a few years before:
http://www.world-nuclear-news.org/newsarticle.aspx?id=12870
Thanks