I bouht an i7 920 about 3 years ago for around $500.
Get a mid-tier to upper tier i7 CPU. I just bought 24GB of DDR3 RAM today from Newegg for $170. That is a pretty good price point in 3 sticks, still have 3 slots to go to 48GB later. (I will actually have 27 GB with 3 x 1GB in the other 3 slots)
Use the basic C: disk for the OS and programs only. Makes it easier to upgrade the OS or restage. I add 2 matched drives, probably 1.5 TB each, for RAW and WORKING files.
A good graphics card will be helpful. Adobe Premiere can use some GPU's quite heavily, but the video cards run from $300 to $2,000 alone! If you aren't doing motion that is overkill.
I will probably buy a GTX 570 card in the fall for around $230 (refurb) or $330 (new - current prices.) That is the lowest level card that is officially certified by Adobe for GPU acceleration for motion.
In the meantine I bought a GT 430 card for $20 after rebate at Newegg today (Normally $70, but sold out now. Low profile version of the same Zotac card is available for $40 after rebate.)
So for parts:
24GB RAM - $170
Graphics - $40 for now
HDD - 2 x $100 = $200 for 1.5 TB or 2 TB each
Plus the basic unit with a power supply (mine is 475 watts) and an i7 CPU. With whatever base HDD they have for the OS, 500GB is plenty. And lowest RAM, because you will likely throw it away if you go to 3 x 8GB chips (the sweet spot right now.) It rarely pays to buy extra RAM or HDD from the manufacturer.
My box is a Dell XPS 435 MT. It is a larger box with a fair amount of expansion space. It has 2 Optical drives (DVD/Bluray), room for 2 additional external facing drives, and room for 3 HDD's internal (I prefer 4 total - 1 OS & Programs, 2 - RAW, 3- WORKING, 4- Documents & Scratch)
I have never paid more than $500 for a desktop without the mobitor, or for a laptop, Just no raeson to! (I bought a 15.4" i5 laptop with 4GB and a 640 HDD last fall for around $425. Great laptop, runs Photoshop fine, etc.)
Sorry, quick post. Not much time.
Have fun!
Michael