Ashton Kutcher -- 'Swatting' Prank Cost City $10,000

The anonymous dumbass who reported a bogus hostage situation at Ashton Kutcher's home this week cost the taxpayers of Los Angeles $10,000 in wasted manpower and other resources -- this according to law enforcement sources.

Law enforcement sources tell TMZ, the emergency teletext -- intended for deaf people as an alternative to 911 -- resulted in a massive police response to Ashton's home, involving dozens of heavily-armed officers.

We're told units from multiple divisions were called to the scene -- hell, the LAPD even dispatched a friggin' helicopter -- all for nothing.

We're told the incident will cost taxpayers at least $10,000 -- though cops are still ascertaining the full extent of squandered resources.

As we reported, whoever sent the teletext message claimed to be locked inside Ashton's home while several armed Russian men robbed the place. The message claimed several shots were fired in the house.

When cops arrived, they discovered the house was occupied by three people -- people working on Ashton's house.