Please, after looking at this, go to the watercooling solved sticky at the top of this forum. Take your time.
BTW, There are many pre-made kits out there. None of them stand up to real watercooling, using the good stuff. The link I gave you is top stuff put into a great selection of parts. Swiftech is just one of the good atuff makers.
Read for a few days before buying anything, the links in the guide will steer you right.
There's really no substitute for using the proper parts rather than the pre-packaged kit. It's not so straightforward, but building your own set-up is not as hard as it sounds provided you do the reading first and take your time to get it right.
Even a numpty like me managed it when I did my first watercooled rig a few years back with no prior experience. $300 should be plenty to set up a decent loop. Be aware that the hardest part for me was summoning the courage to mod my case! That's the advantage those pre-assembled ones have I guess, but they still aren't really as good as a custom one with decent components.
Just finishing up my first WC build. Yep, Conundrum's guide in the stickies is the place to start your research. Just plan everything out in your head before you start, it's not too hard, but I made a few mistakes on my first build despite pouring over every minute detail.
Get your parts list COMPLETELY done ahead of time (it sucks having to paying shipping on one item). I've found Jab Tech and Performance PCs to have good prices and good selection of everything, and they're reasonably priced.
Plan your case layout well in advance (take account for massive GPUs, drives, fans, etc), and drill any necessary holes for filling or draining BEFORE you mount the motherboard. It sucks to get your mobo mounted, then realize you need to drill a hole (cuz metal shavings in the mobo are NOT a good idea)
I would definitely recommend using a T-line for filling/draining over a reservoir. I used an MCRES Rev 2, and it works well, but a T-line has some definite advantages and takes up a lot less space.
I used an HAF 932, works very well, except the pre-drilled fill-port location is in a dumb spot if you're using a reservoir (so go with a T-line).
From what I hear above 4.1/4.2ghz is where it gets dicey.
I've freed up a couple hundred dollars towards my new computer purchase, which is why I've also started to consider going into water cooling. Bought so many computers in my day that it's time to try something new, but research comes first. Will take me a day or two to catch up to the treading given in the stickied guide thread.