TMZ has learned ... former Playboy Playmate Karissa Shannon and her BF, "Smallville" actor Sam Jones, have finally agreed to release their sex tape ... and all it took was cold, hard cash -- that's what she said.
Sources close to the couple tell us they both agreed to a deal with Vivid Entertainment when the offer hit the "six-figure range."
Steven Hirsch -- the president of Vivid -- tells us, "We are excited to finally distribute this amazing DVD. Not only is it extremely kinky for a celeb sex tape, Karissa is absolutely beautiful. And as for Sam, let's just say he's no 'Smallville.' This is sure to be one of our all-time best sellers."
Watch your backs, Paris and Kim K -- sounds like you've got a challenger for the title.