The famous Tyrrell P34 six-wheel Formula 1 car from the seventies, in Model Team style. Includes two working steering axles, V8 engine and seatbelts. Possibly it fits in the current Creator line.
The model is 30,8 cm or 38,5 studs long. Big enough for adding a detailed engine, but not too big, I would consider it medium sized. I mainly used traditional building techniques. As a result, the piece count is not too high, and a possible set wouldn't be very expensive I think.
More information of the real car can be found here: http://www.project34.co.uk/