mongrelEB is correct, I too have done the conversion twice and not needed a different drive shaft. My EA went from 4spd > 5spd > 3spd and I used exactly the same shaft.
Whether you do it yourself or get someone to do it, my biggest recommendation is DO NOT get a 2nd hand box unless you know the history of it/test drive it. Both conversions I have done used 2nd hand boxes and both blew up with in 3 months. It may be more initial outlay of money to get a reco box, but trust me.....it'll save you a lot in the long run!!!
If you get a mechanic to do it, expect to pay closer to $2000. I know my mechanic charges me $55 an hour when I get him to do work for me. Some charge as much as $66 an hour. As far as I'm aware, a manual conversion should take an entire day to complete...Better off doing it yourself, or finding a friend who can do it for you for cheap.