Microsoft is saying is that if you want the free upgrade you need to do it in the first year. After that time you will need to buy the upgrade just like you had to do with every other version of windows. Previous upgrades were around $99 to $129 (depending on version) and I imagine this will continue to be the case.

Microsoft has been heavily promoting the fact that Windows 10 will be a free upgrade for consumers running Windows 7, 8 or Phone 8.1 when the OS is released later this year. While the company is clearly pushing this 'free upgrade' announcement to make sure they can hit their 1 billion users benchmark, ina post on the company's Australian Partner Network, they explicitly state that the free upgrade offer will expire after one year.

Microsoft will offer a free upgrade to Windows 10 for qualified Windows 7, Windows 8 and Windows Phone 8.1 devices in the first year. After the first year, upgrades will be paid via boxed product and VL Upgrades.