The 6 series convertible adds a 3rd convertible to BMW's lineup filling the premium spot at around $70,000. Like the coupe, the convertible is offered only as the 645 which includes a 325hp V8. Based on the roomy 5 series chassis, there is still a usable rear seat left even with the power-operated convertible top. The top features a power-operated glass rear window that works independently of the convertible top. The 645 includes a long list of electronic driving aids including active steering.