it's telling me it's life is done.

last night i noticed a slight squeeling sound while driving, didn't know what to think of it until i noticed that it only did it as the turbo boost gauge entered the yellow boost zone. acceleration is pretty lame under boost. i believe the turbo is caput and either needs a rebuild or a complete replacement. i think it got worse today (i have been staying out of boost to keep it quiet but sometimes, like up hills, it's inevitable) and it pretty much sounds like the tea pot on the stove is ready.
what would my best option be? can it be rebuilt? how much am i looking to spend for a replacement (garrett)? is a mitsubishi turbo compatible without too much hair pulling?