I am creating an arena using command block elements to streamline and improve the combat. I am making use of a scoreboard system to track the number of kills per player. I now want to build a command-based "kill shop" in which a player may trade score for more effective weaponry. To do this, I will need to check that the buying player has enough kill points to purchase an item, remove the points, and give the item or items.
How do I go about making sure a player has at least a certain amount of points, and only then removing an exact number from their scoreboard score?