You have been given several good links to hard drives costing between £30-50, as per your original request. You simply need to click on the 'click here' links in the postings above to be taken to those web sites.
If you specifically want a hard drive of between 10 and 15 GB capacity (I can't think why), you will almost certainly have to buy secondhand. Your local 'free ads' paper, or ebay.co.uk, are a good place to start.
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