Only this one isn't a horse with a horn on its head. It's a privately held startup company that has achieved a rare benchmark of being valued by investors at $1 billion or more. ACV, the online marketplace for used cars that started as one of the early 43North winners, said Tuesday that its latest round of investment funding valued the company at more than $1.5 billion – at least on paper. That's the first time it – or any local startup company – has surpassed the billion-dollar mark in valuation, though well-established Buffalo firms like Delaware North Companies and Rich Products Corp. are already worth far more.