Rack mounted storage

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Why is all rack mounted storage systems so expensive? I know most ones are designed at enterpise and big buisness companies, but even the entry level rack mounted storage solutions start at £1000+.

Reason i ask is that i have been thinking about buying a 12u cabinet to house some cisco gear that i will be getting for my cisco exams, and i was also planning on making a server out of spare parts so i can play around with linux and windows server 2003 to get a hang of it, but to go with all this i want to mount a bit of storage space (2tb+ with some basic redundency incase hdd failure) into the cabinet as well to keep everything together and neat.

The problem is, all rack mountable storage is just silly expensive, whats so special about it? The only cheap option i can see is to use a 4u case for the server i plan to build, which has 6 5.25'' drive bays, allowing me to fit 2 icy box enclosures in it, giving me a max of 10 HDDs. Would using the option i just mentioned give me any problems if i use a good sata raid card along with it?

I, just trying to figure out why anyone, other then companies who desperatly need to efficiently use space, would by dedicated rack mounted storage, when a simple 4u server case can hold 10 hot swapable hdds as it is (13 HDDs in total if you use the 3.5'' bays too)

 

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It wouldnt be running 24/7, and the drives i would use would be for capacity, not speed, so its not like i will be using 15k drives or anything like that. So hopefully the electricity costs shouldnt be too high.

I did have a look at the bay a min ago, but so far i couldnt find anything that would be cheaper then simply putting a couple icy box enclosures into a 4u server case. The ones on the bay that were cheap were just the main enclosures, so i would have to buy the disk caddies seperatly, which could be difficult to source, and could increase the cost to the point where it no longer becomes a cheap solution.