Heidi Montag is privately acknowledging the existence of her sex tape ... TMZ has learned -- and sources close to the former "Hills" star tell us she's finally willing to talk business.
We're told Heidi has agreed to listen to Vivid Entertainment honcho Steve Hirsch when he arrives in Costa Rica to make an offer on the footage ... some of which is said to contain girl-on-girl action with Playboy Playmate Karissa Shannon.
We're told Heidi wants Hirsch to provide her with the sales numbers on Kim Kardashian's sex tape -- which was also released through Vivid -- because Heidi may be interested in working out a "back-end deal" if Steve can't offer enough cash up front to satisfy Montag.
Hirsch told us he's leaving for Costa Rica sometime next week.
Stay tuned ...