I had my turbos rebuilt/ reconditioned recently by CR Turbos ( http://www.crturbos.co.uk ), I cant shout their praises enough, they came back looking like new, with new Steel turbines and wheels etc, circa £800 for the pair inc Tax. or to get them rebuilt to stock is around £500.
Dont forget you need your turbo gasket kit which is £150 from mr T, and your oil and coolant and then your labour for fitting them.. it cost me £1300 in total for it all.
The only reservation I have about second hand turbos is that you could be in the same boat 50 miles down the road
hope this helps