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).
Depends on what you mean by "good." To me, good is something that can run my games without overclocking. To my friend, good is his Alienware laptop. Lucky stiff.
well, I'm getting a good new 1 which would cost between €600,- and €900,- so....that will be abt $700,- to $1000,- for the americans, of course, prices may variate between countries
Go to a local computer store and ask them to build one around your needs. I think a good computer that won't go out of date as fast will cost about $1000, but if you are not a gamer, photo and video editor, you can probably get a good one for around 500-800 bucks.