I would charge for the labor - you know what the hours invovled would be better than us....do not forget to add the time for site prep/layout, POCO time, permit and fees/filing time, etc.
I would also charge for the equipment.
Just because it was paid for once already does not mean it is "free"....it must transported to the site, removed from the site, and stored until the next use. CB's go bad rather quickly on a jobsite/temp. setup vs. permanent in a home/business.
None of this is "free".
What you charge is up to you...a daily...weekly...monthly fee?
Depends on the time-frame it will be used.
Do you have a chart from a rental company?
This may give you some idea of the percentages invovled.