$795 for each turbo from Tischer. $100 for your returned core. About $2000 for the installation I think (someone local in Vancouver did it, and there's a thread but you'll have to search).
No guarantee that new turbos will fix the wastegate rattle though. A lot of people in the US had the dealer replace turbos but the rattle came back soon afterwards. It's just a problem with the design, not because of wear and tear.