I've been looking into upgrading from Windows 7 to Windows 10 this week myself and I've been told that you can still upgrade to Windows 10 for free despite the fact that the Microsoft website says the free upgrade offer expired in 2016. Might be worth looking into before spending any money. I was told to follow the instructions on this page and to input my Windows 7 serial number when prompted.
https://www.microsoft.com/en-au/soft...load/windows10