I know very little of Toyota's so your going to have to fill me in here and there.
What's the power of your current engine, how much does the turbo cost, what gains could you expect with the turbo, how much does the swap cost, what power does the swap make?
Personally... I'd go with a swap. I was considering boosting my 5sfe too.... but I just don't think it would be worth it in the end with such an easy swap. For an MR2 anyways.... for a Celica... it will be a bit more difficult. Camry.... thats a whole nother story.