You can have a seperate "On My Mac" calendar, which stays local. You can then have additional calendars for iCloud—only those calendars will be synced. You don't have to have iCloud activated for calendars to be invited either. Simply create a new "On my Mac" calendar, call it "Work" if you want, and add the event invitations to that.
https://support.apple.com/kb/ph2682?locale=en_US
Update:
As mentioned in my comment below. If you have an existing local calendar e.g. "On My Mac" or "On My iPad" and you sign into iCloud, you will be asked "What would you like to do with your existing calendars". Click Cancel to keep your existing local calendar.
The local calendar has to exist before signing into iCloud. I couldn't find a way to add a local calendar if already signed into iCloud.
You will now be able to create a "Work" iCloud calendar and access the shared iCloud calendar. You will also have the private local calendar.