If your thinking about buying a xbox HDD form hong kong beware they are fake.
The HDD case is bought of the internet for £12.99 and you get a choice of colours for modchipfitters and the Hard drive (WD Scorpio 120GB Hard Drive) it self is bought for about £24. You can search the net for both of these and buy really cheap. You also need to add some info to the HDD Called. hddss.bin which is avaliable to download off the net When buying u will usually find that the casing has been badly sealed and they will not connect to the XBOX 360 console With out physical force, Or use of tools which will in turn damage your Console and most like VOID your warranty. If you really want to buy one check the feedback and you will usually see alot of "received damaged" comments left. As they where put together by hand and damaged as no care was taken. Plus there is no warranty with these.
Its your money. So good luck
Contact me if you need any info on where to get the items and ill try to help you out.