I need Office and there is no alternative
Libre Office comes standard with Linux. Although not 100% you can open almost any MS-Windows Word or Excel doc but we recommend to convert your documents to Open Office / Libre Office.
Collaboration can only be done with outlook
Email has been around before outlook and combining a few server services and you can get most of what a company would require like shared contacts using LDAP and Thunderbird mail Client etc.
We do everything in Excel and that does not work in Linux.
With Libre office you can seamlessly open and import Excel files and Libre office come as a default installation saving you Installation time.
The cost of training is too high.
Nonsense, we have found that the users require the same amount of training than Windows users and not only that some of the users are barely computer literate.