You mean the 'Mk3.5' cabrio?! There was never a cabrio actually based on the Mk4, and the one you are talking about is simply a Mk3 cabrio with a Mk4 look front end and dash. The advantage to this is that the parts are mostly interchangeable with the Mk3, so yes the nice steering wheel will fit and the airbag will plug in. Costs - I believe you are looking at around ?500 from VW... You might find one in a scrappy if you are lucky, but of course the airbag may well have deployed!