What are my lighting options for a pole-barn garage?
I'd probably try for a mix of natural light, fluorescent, and point lights.

The natural light will be the most economical, but obviously fails at night.

The fluorescent lighting should give you enough light for most working conditions.

And the point lights should help for when you need to do detail work or get under the hood of your cars. You can find point lights on articulated arms, that way you can just grab and move the light to wherever you need it. Mounting an arm or two on each pole would probably be enough.