The biggest problem is that clients WANT Microsoft Office. You can offer them something else (Apple iWork, Lotus Symphony, Open Office, LibreOffice, KOffice). It can do everything they need and they will still argue that MS Office is what they want because of a myriad of factors (training, familiarity, computability, etc).

Some people might be able to shave off some customers, but you are going to have to have some killer feature (even if it is price).