It depends a lot on what you need. A really fast computer suitable for the latest 3D games with all the latest hardware might cost 15000-20000 SEK, but you can get a fairly okay computer for under 10000.. maybe as low as 5000.
You can look at for example
www.dell.se for some ideas, they have fairly good prices as far as I know. I just looked and they had 2 computer packages for around 7000 that were pretty good. There may be some even cheaper ones if you look around (or look at different computer selling sites).