As well as OpenOffice
there's also LibreOffice
; for the vast majority of word processing you'll barely notice a difference between the two but Libre is updated somewhat more frequently and has a number of functions I find useful.
Both give you pretty much all the functionality of Microsoft Office (especially the word processing) but for free. As Valthazar mentions you'll need to make sure you do a "save as" and change the file type to .doc/.docx if you want people who use Word to be able to display your files but otherwise there's no real drawbacks.
The change of Microsoft Office to a subscription format is known as Office 365 and follows a trend within software licensing to move to a recurring rather than one-off payment model. I don't have access to the US site but on the UK one you can still buy office as a one-off (the basic version containing Word, Excel, PowerPoint, OneNote is £110). Perhaps of more use to you may be Office Online; it's an online Microsoft Office suite that's free; although I don't use it so I can't attest to its usability.
As you're a student Valthazar's mention of buying Word through your college is a good option to look at. Alternatively Microsoft also offer a student version of Office 365 (at least in the UK) which gives you four years of a full Office Suite (and some other benefits) for £60.