Buying parts seperatly is the cheapest way to go.
Go on ebay and look up heatcores and buy one for a car / plane / whatever, get it, attach barbs. - $20 - 25 with barbs
Buy a big pump (Enheim, Rio, etc) - $40- $50
Buy a good waterblock - $45
Tubing, clamps, misc - $10
Tupperware to make a resivor - $5
Total: $120, with better cooling then any of the premade ones.
Or see what you can pick up the in the forums, people usually have good deals on waterblocks and the like.