It seems that when a well known company is bought ought in the tech space reporters very often find out the purchase price.
Both the purchaser and the company getting acquired publicly state that they won't disclose the price, but we usually get it nonetheless.
If we take Wufoo for example, they have a handful of people on their leadership team, and although Survey Monkey has 60 ppl, I'd bet that only a handful of people were involved in the details of the transaction.
I have a suspicion that it is usually the company being acquired that leaks this info to a reporter with an understanding of source confidentiality. Or is this info coming to reporters from third parties that were involved in the deal?