Well it depends on who does the due diligence. Sometimes it can be people from the acquiring company, this can be relatively cheap. Sometimes it can be a 3rd

Well it depends on who does the due diligence. Sometimes it can be people from the acquiring company, this can be relatively cheap. Sometimes it can be a 3rd party brought in, usually I-Bankers. This can be expensive, up to 5% of the purchase price. Another fee that can be expensive is the break fee. This is a fee paid to the acquired company if the deal falls through. This is supposed to prevent the acquirer from getting a thorough look at their competitors books and then walking away. Typically a break up fee can be 10% of the acquiring price, though in the Google-Motorola acquisition I heard that it's 20% of the purchase price.