I need some help understanding turbos

First off car is MY00 PPP with full decat probably around 270bhp.
It has recently developed a whistle when under load- I'm lead to believe this could be the bearings in the turbo. I assume it has a TD04. Am getting it serviced next week so should know more then.

If it is the turbo do I:

1 Take it off the car and get it serviced, cleaned and refurbed- cost about 300?
2 Buy a second hand TD04? - 150-200?
3 Buy another turbo (second hand or new?). If I do this what can I buy that will bolt straight on without any other mods that would be an improvement?
What sort of cost is this?

Also what are peoples thoughts about buying 2nd hand turbos? Can you tell what they are like condition wise before fitting?

Thanks in advance.

 

are you sure you havent got an air leak somewhere would have thought that the speed of the turbo that if the bearings where making a noise through wear they wouldnt last 5 mins
as for buying a 2nd hand turbo why go through all the hassle