I agree with the above suggestions. Apache OpenOffice is very popular and office compatible and Google docs / spreadsheet is getting more popular among the business types.
Other options include: Lotus Symphony and LibreOffice (fork of OpenOffice).
If you are talking about pirating Excel, there are torrents available but: 1) you risk virus/malware infection and 2) Microsoft is pretty good at detecting and disabling pirated software. At the very least you will not likely be able to apply updates.
