Holding a training session without payment is a violation of the FLSA regardless if it is agreed on or not.
One additional four hour firearm's training session would cost my department in the area of 16 to 18k. Not inconsequential. Add to that the other eight to ten mandated in-service training sessions and it strains the budget.
A significant, and certainly understandable, impediment.
Then again, how much will it cost to defend the town and officer(s) in a lawsuit alleging inadequate training, negligence, excessive force, etc. should someone be killed or injured by a misplaced or unwarranted shot?