Flashbangs are a thrown, non-lethal weapon that first appeared in Grand Theft Auto: Chinatown Wars and are due to appear in Grand Theft Auto VI. In their prior appearance they were sold at Ammu-Nation for $150 per set of eight canisters once unlocked, taking the form of a generic grey cylinder, visually similar to Tear Gas, that stuns anyone caught nearby. No pricing or vendor details have yet been revealed for their Grand Theft Auto VI incarnation.
Weapon data via GTA Wiki (Fandom), CC BY-SA 3.0.