Agreed, but once you have put and OS and then and some software there is not much left for anything else. You can get 1TB SSD's but they are about £1.4k. Better to get a smallish SSD for your OS and programs then a standard HD for data.
What do you plan on doing with it and what do you call small? The main problem with small cases is you are limited with a number of things. Firstly the size means the motherboard you want may not fit. Likewise expansion cards may not fit. Lastly you can also face issues with keeping it cool...
SSD are not really worth the money unless you want a PC that boots up very quickly. Unless you are using software that needs to read / write a lot from the hard drive then you will not notice the difference once it is booted.
I built my current PC. Brought the bits from eBuyer for just under £600 including Windows 7. Like others have said building it is not hard and there are loads of guides out there that talk you through the process. Took me about an hour to put together. Takes longer to install the Operating...