Dana White's all about a fair price ... handing out hundos to a fan who tried to give him rare memorabalia for free -- and, flexing a wad of cash while doing it.

The CEO and president of UFC was at Fanatics Fest -- a multi-day festival featuring some of the top athletes and sports personalities in the world -- when a fan came up to take a quick pic with him.

Turns out the fan -- a guy named Kenny Duncan Jr. -- is the founder of Celebrity Mint, a company that makes commermorative coins, shaped like trading cards, of legendary sports figures ... and, he offered a pure gold coin featuring Mike Tyson for free.

Dana could've take the card and run -- but, he refused to accept without giving him a little something ... ulatimately whipping out a fat stack of cash and peeling off $600 in exchange for the .5 gram coin.

Dana -- who's tight with "Iron Mike" -- puts the money in Kenny's hand and heads off ... a welcome surpise for Kenny who was ready to give the card away.

Celebrity Mint's got other stars beside Tyson BTW ... featuring stars like Floyd Mayweather, Ric Flair and Pete Rose -- athletes certainly worth of being cast in gold.

Dana's one of the hardest working guys in sports ... and, clearly, he ain't trying to take advantage of anyone!