If the case fans will cool your system sufficiently when running at 7v (and there are several ways to get them down to 7V) you do not need to replace them. It all depends on whether you OC, how air flows in your system, and what temps you are willing to live with.
There are three primary noise sources to deal with once you've done the easy work on the case fans. The chipset and GPU fans are almost always noisy, and the CPU fan can be noisy if you do not have something like Cool n Quiet enabled.
As for the chipset, I've been very happy with the Zalman NB47J in a prior system or two. That said, I would not be in a rush to get it, depending on just how your mobo is laid out.
From your prior posts, it looks like you may already have decided against the 47J, but if not, let me throw out another warning. My mobo is a DFI NF4 Ultra D. The board has a great rep among OC'ers, but the pretty little chipset fan gets all sorts of bad mentions. When I spec'd out this current system, I bought a 47J and got rid of the chipset fan. When I went to install the 6800GS video card, it was clear that the overhang of the card and the height of the 47J would never play nice together, and that it was far more than just bending a few pins.
Generally, the faster the card, the bigger the card, and the bigger the card the more overhang. Your 7800 is almost certainly bigger than my 6800. If yours goes right over or near the center of the chipset, and if it hangs as low or lower than my 6800, plan on spending a few hours bending fins, but with no guarantee it is is ever going to fit short of actually removing fins.
In my case, I was able to move the card to a second PCI-E slot (my board is not officially an SLI board, but it is easily SLI moddable) and get around the problem that way. That solved that problem, but moving the video card created other problems I won't go into here.
I had to take my system completely apart because neither the Sunbeam nor the Zalman fan controllers I'd bought would install in my screwless case, a Thermaltake Tsunami Dream. The Sunbeam had other problems, too, but that is another story. I decided to replace the GPU fan with the VF-700 at the same time I replaced the fan controller with a Thermaltake Hardcano 12. I also bought the shorter Zalman 32J to permit me to move the video card back to where it belonged.
It does not work. Even with a couple dozen bent fins, the 6800GS will not seat in the top PCI-E slot.
The moral: YOUR MILEAGE MAY VARY.
Right now, I've put the stock chipset fan back in place, but put it on the fan controller, which has decided to run it at minimum voltage. It is 6 degrees cooler than was the 47J under light surf conditions.
I've read of a couple replacement fans that can be made to work on my board that are supposedly more quiet and reliable than my stock fan, though not always easy to install. They may be a good option for you as well but, unfortunately, I do not recall any search terms to help you find them.
As for GPUs, the NF700 warns that it usually takes away an adjacent PCI slot, but with a 7800, you probably already have that issue.
For CPUs, the Zalman 9500 is an attractive and elegent solution. The Ninja may be a tiny bit better, but I do not think it is attractive. Neither is cheap. The SI-90 with a big fan bolted on the side is the favored cheap method of cooling a CPU. It is not pretty, but it works pretty much as well as any more expensive solution to the problem. Given your overall budget, it may be your best choice.
Newegg is the obvious source for anything, but if you are buying multiple small items, their shipping charges can really destroy your budget. Look for a source that ships by weight rather than item count.
Good luck!