I think you need to look into cooling concepts a bit more. You say 10C, but that 50F, which is unrealistic for normal room temperatures. The true measure of a system is the difference between the CPU/GPU/chip temperature and the ambient temperature. A poor stock air cooler on a 470GTX will run at 90C while the room may be at 20C. This is a 70C difference in the air coming into the case and the temperature of the GPU. Even with the best water cooling in the world, we aren't going to get below 20C.
Liquid cooling allows for a large contact area with air because it allows the user to place the heat exchanger anywhere they please. This allows for larger coolers to be used. The water is simply the medium which transfers the heat to the water/air heat exchanger.
This is a key concept to understand. Unless you chill your water somewhere in your loop, you aren't going to get sub-room temperatures.
EDIT: To answer your question haha... A good liquid cooling system will cost nothing near the price of a Mac Pro (these top out at 5K.) You can get a high quality full loop with GPU, CPU, and even chipset block with radiator, pump, reservoir, control panel, fittings, tubing, additives, and fans for around $500-600. Buying all the most expensive gear doesn't always give you the best results. It really depends on the build. You need to consider getting a watercooling designed case such as the Corsair 800D or a modified Lian-Li. These range from 160 (HAF X) to 500+ (Some Lian Li's).
This is only for the cooling gear and case. You then buy all the computer components you need such as the CPU, GPU, PSU, RAM, HDD, disk drives, mobo, etc. A great combo would be 2600k, 580gtx, 8GB ram, Z68 mother board, etc. This will run around 1,200-1,500. So for right at 2-2.5K for a top of the line liquid cooled system from scratch.
