My friend and i were playing the other night. He activated expose on his VT49. I take a range 3 shot at it. Does he get the +1 agility cause of range 3 or does it stay 0 cause Expose technically would take his agility to -1. Thanks for the help!

When you activate Expose, as part of the cost you lower your agility by 1. You can't go lower than 0, so the cost is paid.

If, later, you are at range 3 or behind an asteroid, you get the bonus.

Does he get the +1 agility cause of range 3 ...

Range 3 (primary weapon) does not change agility. It adds one defense die.

Wedge with outmaneuver attacks a VT-49 with expose at range three through an asteroid. The target rolls zero defense dice for agility plus one defense die for range 3 plus one defense die for obstruction. That's a total of two defense dice.