To get youself a second hand turbo which on this car woujld be a K03 you would be looking at £100 i would think for a fearly good one. But if you have to take the turbo off i would realy sagest going for K03s one. Thesesa re about £250 second hand but will be a much better upgrade to the Golf. You will then be looking at about another £80ish + or - a few £ for washers, gas gets, coolent etc to be replaced.
So would say to play it safe to do a turbo swap, bugget on around £330 and thats doing the job youself. Hope that helps mate.