You will probably get much better answers in the water cooling section of the forums, but I'll start you off.
To fit water cooling in a case, you need to plan out exactly where everything will go. If it turns out that you do not have enough room in your current case, get a bigger case or build an external cooling system.
Now for parts:
automotive heater core: $20 (radiator)
tygon tubing: $20 (or vinyl tubing from home depot for much cheaper, but not as good)
waterblock: search around for a good price. Classifieds here are always selling them. Or get one new for $45
pump: eheim 1048 or 1250 - $40-$50. Or you can go cheap with an attwood v500 bilge pump for $15, but it is not designed to last as long and it needs to be submerged so you will need a reservoir.
epoxy, goop, hose clamps, barbs, screws, etc: $25
fans: $10-$20
Also, a great tool to have for any modifications is a dremel. That will run you $50, but you don't necessarily need it. It's just nice to have.
Wow, now that I'm looking at everything here, Hoots case that he sold last week was one helluva deal...
