Original 'E.T.' Movie Poster Art Going for SIX Figures!

The art that became the iconic poster for "E.T. the Extra-Terrestrial" is hittin' the auction block, and it ain't gonna be cheap ... as in you'll have to trade in a car -- or 2 or 3 -- just to make a bid.

Heritage Auctions is selling the original art piece, which was painted by famed artist John Alvin -- who's also done art for "Star Wars," "The Goonies," "Blazing Saddles" and a bunch of other hit movies. We're told it should rake in $150,000 ... at the bare minimum.

At first, the piece belonged to Hollywood producer Bob Bendetson, who got it directly from Universal Studios years ago. It was hanging in his office for years, but now that his wife's turning that into a guest room -- he's ditching 'E.T.'

The artwork goes on the block October 12th. If you're on a budget, there's always the knockoff poster.