It's no small amount to be shelling out over nothing, but since this isn't nothing, per se, Barrow is just relieved to pay the idiot tax instead of fighting, or worse, spending time in a cell and having to get Riftwatch to bust him out.

"There you are," he informs the guards as he drops the requested amount in the younger one's palm, "see? Here she is now. We'll just be on our way, then."

Glancing back to Astrid, he feigns annoyance, but there's a playful glimmer in his eye. Good thinking.