There is no saving money with Microsoft. You will paid with your airtime, privacy violation, patience (as second official release looks like a beta), lose of productivity, as when you restart Windows it will tell you "Do not power off, Windows is updating system files". So you wait one hour for Windows to finish. It happened to me with laptop on the road. I turned it on for quick Email checking and was stuck with this message, battery was completely depleted. This is how Microsoft takes customers seriously.
There is no official 'free' upgrade from Vista, but Microsoft wants you to join for 'telemetry'. For this reason they silently accept upgrade from XP/Vista and don't do checking SLIC in BIOS after upgrading from Windows 7. So if you want to go this route do the following:
1. Install a fresh installation of Windows 7 Ultimate SP1 without Internet connection. Skip serial number prompt. ISO can be downloaded from Microsoft. You can use a spare hard drive, disconnect old one, it will be easy to go back.

No joking.
2. Install DAZ loader, reboot.
3. Validate online (it is important).
4. In Windows 7 run setup from Windows 10 Pro ISO. Do not do online upgrade, it is buggy. Do not enter any key during installation.
5. Activate Windows 10 online, make Microsoft happy.
If you ever want a fresh installation of Windows 10, do not enter any key, it will be validated, as your motherboard is registered on Microsoft servers.