Dangerden has some of the best stuff available. If you think the prices are to high at least get a Maze-2 water block and go elsewhere for the rest of the parts. The best way to save money is to be creative and use whatever you can scrounge up. If you go to a junkyard I'm sure you can find a radiator for almost nothing.
One thing I highly recommend doing if you build your own system is to install an in-line thermal probe with the water. This way you can find the temp of the water just before it enters the waterblock, and you can also see how well your radiator is working.