Oh boy, Where do I begin? If your planning on building it by your self: http://www.buildacomputerguide.com/, As well as google searching some products such as CPUs, GPUs, Mother boards, Cases etc. Will be cheaper for you, And no extra charge Bull S***
If you want to have a company give you full costumiability and have THEM build it for you and ship it to you with your choice of everything, Check out some sites/company's such as Origin PCs, Alien Ware (Dont recommend though, Over priced IMO) Velocity Micro Etc etc. Just look around on google, However if you have them build one for you, you'll have to pay extra,
Hope this helps, I'm not really an expert on the whole subject. JAM.