The windows 8 Pro came pre-installed on my new SONY VAOI laptop (OEM). I'd like to go back to Windows 7 (as I'm very unhappy with windows 8) but Microsoft wants me to buy a new license ($140) This is unacceptable. I want to downgrade for free. I want a Windows 7 DVD (or link to download it) and I want a valid product key. Is it too much to ask ?

According to the Microsoft OEM License website, all windows 8 OEM is eligible for downgrade rights.
Windows 8 Pro includes downgrade rights to Windows 7 Professional
However you need to obtain a "genuine Windows media" (also called a DVD) and a valid product key. So I call SONY first , they said, you have to get a windows 7 pro DVD and then call Microsoft to get the product key.

So I called Microsoft and of course they refused to give me a product key.

http://www.microsoft.com/oem/en/licensing/sblicensing/pages/downgrade_rights.aspx#windows