Dana White is building a personal weapons room in his Vegas mansion (seriously) ... so he hit up the guys from "Pawn Stars" to buy a REAL combat-used samurai sword.
The UFC boss had a hard bargaining sesh with Chumlee and Big Hoss over a whole batch of blades -- which the guys claim can be traced back to the families of the samurais who used them.
And in a matchup of equally intimidating bald dudes, Dana and Rick Harrison negotiated for the final sword -- bringing his total bill to $69k.
White made hundreds of millions on the UFC sale -- so we think he'll be alright.
The real question ... what's Dana adding to his playhouse of destruction next?!