Charlie Sheen For Insane Clown Gathering

ICP member Violent J tells TMZ ... the group received a call from Charlie's rep back in April ... telling them how Sheen was a HUGE fan of the Gathering and he would LOVE to work with the group.

Of course, ICP was STOKED -- but figured Sheen was WAYYYYY out of their price range. But, Violent J says Charlie was "so into the message of the festival" ... they were able to agree on a "reasonable amount."

The deal was finalized last week and Sheen will serve as an M.C. at the event in August.