Had mine done by a firm called Turbo Dynamics Ltd at Christchurch. I've got no connection at all with the firm except as a customer but they were quick & did a fair price but what I liked best was that they sent a data sheet with all the balances, tolerances etc of the rebuilt units so you could see how they had done the work. 12 month warranty. I think it was about £300 for a turbo on a 300hp engine.
www.turboclinic.co.uk best and most economical service I have ever had on my Torbos. There was some talk that he may be selling up but worth a check. Oh if you do have the Turbos refurbished send the oil supply pipe as well as it is imperitive that it is clear and has to be down to them if its not and you have problems. its not easy to tell if its partially blocked.
best of luck