Find a friend who goes to a college that participates in the MSDNAA system (or attend one yourself). I don't remember if Office is part of that, but, if it is, they can toss you an activation key for free. Err. For educational purposes only. Okay? You can also ask around for any friends that might work in a business that provides it or sells it to employees at a lower cost. You can also use Office Online for free anyway.... Otherwise, just use one of the dozens of alternatives available online for free.
Not free and not office 365, but if you have a .edu mail address you can get office 2016 pro for $9. Google Microsoft Home Use Program...The good thing is that you get it for life and not subscription based like 365.
Certain colleges and universities give students a free or discounted download of Microsoft Office. There are also free alternatives to Microsoft Office like OpenOffice and LibreOffice that can be downloaded, but I have never used any of those an can't be certain how similar they are to MOffice. Then there are the cloud-based versions like the GoogleDrive and Microsoft OnerDrive based ones. The only down side to these ones is that you need internet access to use it. So if you need it for a laptop I recommend downloading one of the free alternatives (try multiple and find the one you like) even if you mainly use the cloud-based versions. You don't want to find yourself in the situation where you need to work on a report and there is no Wifi/Internet. If it is for a desktop you will probably be fine without a downloaded alternative since you usually don't have internet issues with desktops but it also wouldn't hurt to have a backup plan for random moments you internet connection dies on you.
I can get you Home and Business 2016 for about 100 USD. Buddy of mine can get you Professional Plus 2016 for 60 USD.
A legit, unused Pro Plus perpetual license? What about with a disc from MS? I use to get those through my old workplace for about $20. But $60 isnt bad either.