It's all good and don't worry about it if you don't have much experience with water cooling yet - we all have to start somewhere - and you're going about it the right way by comng to the forums and picking peoples brains...
Well, it's called buyer beware - you get what you pay for. For the CPU, you can go cheap but you won't get as good performance. I'd say that the best out there is going to be either the Fuzion or the Apogee GTX for your CPU. You'll pay between $50 - $70 for either depending where you go.
For the GPU, stay away from the fullbody waterblocks like those made by DangerDen, EK, Koolance, etc. They kill flowrates in a cooling loop because of the many bends and tight turns. They are, also, the more expensive blocks. Stick with the GPU core exclusive models like the DangerDen maze4, Fuzion, MCW60 and the Stealth. They'll run you anywhere from about $45 - $110 (as opposed to $100 - $140 for the full body blocks).
memory and northbridge cooling are novelties and don't really need to be watercooled as a decent hsf or a good airflow in your case would suffice. The only instance I would cool a northbridge is if I did some way serious o'clocking. The northbridge handles communication between the various PCI lanes (PCIe, PCI, etc) and the CPU as well as all memory communications between the CPU, your CPU cache and your system memory on Intel configurations (and only system memory on AMD machines as they have their meory controller directly on the CPU). So, you see, if you don't really do serious o'clocking then just stick to a decent hsf for the NB.
There you have it, a half decent argument why you only need worry about the CPU and GPU - that should cut down on some expenses.