2002 Laguna DCi turbo problem?

Hi folks.Hope someone can help .......My '02 laguna 1.9 dci's turbo is a bit noisy(sounds like a semi distant police siren on acceleration)and when I boot it I get a BIG plume of black smoke,after the initial burst of smoke it gets a bit better-not good for the environment or emission test.I fear its on its last legs. Can this be fixed without major expense e.g. is there another turbo from another vehicle/make I could swap for or can you repair/refurb a turbo yourself ? PLease help- I love my car but its running costs are getting me down.