What stops weapons from spawning?

When the cost sum of all spawned weapons reaches a cap, spawning pauses. When all six spawn points are filled, spawning also stops. For example, if you have a Viper (5), a Hammer (3) and Wildcat (3) spawned your total is 11. If a Super Majestic then spawns, your total is now 21 and the spawning stops because the current cap is at 27.