James, whilst the guy at scorpio might know about computers I doubt he knows about TS2013---the game doesn't exactly fit in with how PC specs are supposed to work, and as nick has just posted the game demands a decent CPU, with the i5 family giving the best 'bang per buck' as it were.
sargnickfury wrote:keeping steam on separate drive is always a good idea for better performance.)
is something I fully agree with, whether that be an SSD or a conventional (much cheaper) spinning drive it's well worth the money---£40 gets you a Terrabyte of storage space these days, maybe even more if you shop around, so it's a pretty cheap way to get a performance boost.
As you have a keyboard, mouse and monitor you don't need to buy these agin so all your budget can go on the 'magic box' itself,
http://www.aria.co.uk/Systems/Home+and+ ... ctId=55872 whilst being *only* an i3 and not having a discrete GPU is a good starting point---cheaper than your quote too. If you phone round places like Aria and see what they can change in a spec to suit YOU rather than a supplier telling YOU what you need you'll end up with a much better machine.
GPU wise, nVidia are favoured and whilst a GTX 870 would be nice (I'm not jealous....honest.......) I'd suggest you start looking at the GTX550 range (about 100 quid for a 550Ti) , and move up if the budget allows.