M134 Minigun (from Terminator 2, The Matrix, Bee Movie, every other high-budget action movie, etc.)

This weapon fires $200 custom-tooled cartridges at over 7,500 rounds per minute... It costs $300,000 to fire this weapon for 12 seconds Finally got around to clocking the approximate firerate of this monstrosity and, well, it's pretty gnarly. You'll dump a whole 750 round belt in about 6 seconds if you hold down mouse1. What's not to love!