Robin Williams -- Turned Down HUGE Vegas Offer

Robin Williams turned down a huge Las Vegas offer 2 years before he died ... and sources connected with Robin tell us it's further proof he did NOT have money troubles.

TMZ has obtained an AEG Live document to Robin ... offering him $600,000 to headline 2 shows at The Colosseum at Caesars Palace.

We're told Robin's people turned the offer down ... he was shooting "The Crazy Ones" at the time. Robin's people -- who have maintained all along money was not a factor in his suicide -- tell TMZ if he was really cash-strapped he would have done some moonlighting in Vegas to rake in some dough.

Under the proposal ... ticket prices ranged from $75 - $150.