Pricewise & partwise. I just started doing my initial research and the tons of parts available are mind boggling. I'm looking for decent overclocking room. I don't want to oc the cpu to 7ghz. That's insane. No no, I'm just looking for better than aftermarket air temps. I don't like the noise my tower makes right now. 6x120mm fans are errr...not the quietest. I'd like to keep it all under 350-400 as I'm looking to purchase a new case as well. Hopefully a HAF 932
The GPU covers alone will be $90+ each. A good pump/res about $100. Good CPU block $50 up to $75. Rad? You'll be needing a 120x4 or possibly a 140x3 at a minimum, another $100+. Add in fittings, hose, and fans another easy $50.
If your really looking for big overclocks, you'll want two rads and two pumps for two seperate loops, CPu on one, GPU on another.
Start with the 'watercooling solved' at the top of this page.