See what Reuters reports:-
http://www.reuters.com/article/2012/09/14/sony-olympus-idUSL3E8KE33C20120914
They would possibly spend 50 Billion Japanese Yens, i.e., 646 Million US Dollars, to buy for a stake.
Via 1001 Noisy Cameras.
By the way, it seems that Sony is more than ambitious to control the whole digital camera industry. If this acquisition comes true, Sony has almost controlled most of the mirrorless market, for both the 4/3 and NEX. And then actually they have virtually full control on Nikon via the supplies of sensors for their cameras. The only enemy left is just Canon but it also seems that this enemy would be beaten in the future!
Let's see what will happen for the years to come! Reality is really cruel and competition is always fierce. Only the strongest will survive. That's still the law of nature.