LibreOffice is a free, open-source, powerful office suite software that is a great alternative to Microsoft Office. I use it on my home computers. It is available for Windows, Mac and Linux and has six applications: Write (word processor), Calc (spreadsheet), Impress (presentation), Draw, Math and Base (database). It works great and the menu functions are similar to Office 97, so the learning curve is easy. It is built off of the same code base as OpenOffice. I happen to like LibreOffice better and think it runs faster.
One of the great features is that it can open, and save as, files in a variety of formats including Microsoft Office (multiple versions), PDF, ODF, and more. I have mine automatically set to load and save as MS Office files so that they work at school without a problem.
Support is excellent, with a great support site and user forums.
The upgrades include built-in grammar checker and a real time work count window for Writer, ability ti embed multimedia in Impress, and increasing Calc's sheet count up to 10,000 per workbook. That's a spreadsheet I do not want to work with. There are quite a few other upgrades too.
Instead of spending hundreds of dollars on office software, download LibreOffice for free. http://www.libreoffice.org/
Free Alternatives to Microsoft Office
Why do schools still pay so much for software? Free alternatives to paid software and services.
Google for Educators resources (includes Google Docs)