At the time of writing (1st May 2013), Dell UK are doing a special deal on some of their file servers. As they are one of the 'big three' server suppliers, make good boxes and have a very convenient online ordering system, it's worth considering. For instance, the entry level Dell PowerEdge T110 II starts at just £249 (it's usually £453). It comes with a single 500GB hard drive. That's not very much storage these days, plus it's common to have more than one drive for redundancy or backup. So let's add another 500GB drive; the price for that is another £164. If you think that's rather steep for just 500GB you're right.
Last couple of times we opened up a PowerEdge T110 II it contained Western Digital Caviar Black drives. These are rated as 'enterprise' drives; they are extra reliable and relatively high performance, specifically intended for use in file servers. That means they are a bit more expensive than regular drives, but not that much. Specifically, a 500GB Caviar Black costs £57 at eBuyer. Actually that's £57 including VAT whereas Dell's £164 price excludes VAT, meaning that the same drive from Dell costs three times as much!
Looking at things from a different angle, if you could buy the T110 II without a drive at all it would be just £85! (i.e. £249 minus £164). That would be the bargain of the decade; unfortunately, they won't let you do that.
We'll re-emphasise that overall this is a good price for a entry level server from a proven, quality manufacturer. But a cynic might well think that Dell are using very high prices on hard drives to create a possibly misleading view on the price of their kit.