Charlie Sheen -- I'm Rockin' a $3,000 Mask for Halloween!

Charlie Sheen's Halloween costume is WAYYYY more expensive than yours ... and the crazy part is, he's going as himself.

Sheen was in L.A. earlier today working on a new Roman Coppola project ... when he bragged about an unbelievably lifelike Charlie Sheen mask he got from an artist in Colorado.

We're told Charlie heard about the mask a few months ago, and told the artist, Landon Meier, that he would give his stamp of approval ... if Landon gave him one for free.

The artist came through ... and Charlie wins again.