Over the past few months I have purchased 3 copies of MS Office 2016 Professional Plus for £38.50 each.
The first one for my computer - the others for family members who lean on me for computer advice.
I was a bit sceptical at first - you read so much about scams on the internet. But it was fine, and I obtained a genuine download complete with a proper product key which was activated by Microsoft when I installed it. The other two purchases went just as smoothly.
I obtained them from here (From where you can also obtain various versions of Windows - including Windows 10):-
Office 2016 - UniqSoftwareThey have customer support offices in US/Canada and Australia but are based in London UK as official Microsoft Partners