Microsoft as of today is no longer shipping Windows 7 to the big OEM computer makers anymore. This means the chances of you finding a Windows 7 machine..or even a win 10 machine with “downgrade rights” to Windows 7 stop existing as well. If you want a real downgrade take windows 10 back to windows 8. I thought that would make you shiver..:)
How do you avoid the Windows 10 mess? You will have to talk to your local tech(or in my case your local Microsoft partner) who can still get legal copies of Windows 7. I cannot build you a computer for the costs the big guys can as I do not buy parts by the trainload. What you will get is a system built to your specifications with the operating system you want. Keep in mind Windows 7 fully dies in January of 2020 so the reprieve is only temporary. Of course “supported” hardware may run out faster so Windows 10 is in your near future. Unless you REALLY want to deal with Windows 8. If you hate Windows 10 enough you might..:) The time to build your new PC is now if you want to stay on Windows 7. The “older” cpus that will be supported are going to dry up quick. It is a horserace to see which one runs out first. Windows 7 availability or the CPU parts that will be supported by Microsoft to run Windows 7. I think both will run out pretty quickly.