What to know how much, if any we would save on changing 240v highbay lighting to 277V. The ballast are multi tapped so we would only have to change one wire. How much would we save per light fixture.

You wouldn't save anything. You are not changing the system wattage of the fixture.

The taps on a multitap ballast are for the various input voltages. If you change the tap from 240 to 277 volts, the fixture will not operate properly.

And noma is correct, your not changing the wattage of the fixture.

Thank y'all.

Besides, you can't just change from 240v to 277v just like that.
277/480v is a completely different system from 120/240 or 120/208.
You'd have to re-route the feeders to a different panel, and you would obviously need 277/480 v on site.