Well of coarse the kit will be more expensive, you're paying for coninienve. If you dont have the time to build one or just don't want to, what's wrong with paying a little extra for a pre-built kit?
Ok.......to clarify a couple things. No matter what dude, you have to piece it together. You will get tubing, the blocks, pump and a radiator and guess what, you piece it together yourself. It's not 'prebuilt', it's the fact they have all the parts (crappy ones) available in one package.
Going to www.dangerden.com
and buying tubing, pump, block, and radiator in one go is no different than buying on of these 'kits' as it'll arrive in pieces and you will have to put it together, but one (the dangerden one ) will be of superior quality and performance.
There is no such thing as "A good beginners kit" as no matter what, you will have the parts seperated, you will need to put them together, and you will need to leaktest your rig.
If you're going to go watercooling, dont mess around with prepackaged crap, go to www.dangerden.com
and get your parts from ther, or if you're not in the US some other place that sells parts like it.
Listen to gaara's list or go to www.xtremesystems.org
or .com now I think they've moved to and ask some questions there but you will get similar answers all around for a 'generic' kit which is usually 1/2" tubing, a TDX block, and a D5 pump and a couple suggestions will be given as far as a radiator or heatercore goes.
Needless to say they also look much nicer than a old car heatercore.
So paint it......it's not that hard. Or you can contact people like "Weapon" at xtremesystems who mods them out, paints them, and builds a shroud for you for a certain price.