diazalon :
Thanks for that! How many mm of radiator do I need. Is a 60mm thick 240mm enough to keep it cool? How much would it cost to watercool this(amazon.com) for everything?
That depends if you also want to include the CPU as well, but yes. A 240mm radiator with that thickness should easily handle the GTX 780 and a decent CPU as well. Just remember to put some high static pressure fans on the radiator, so you can move the heat away from the radiator.
It really depends on a lot of things, prices on tubing, blocks, radiators, fans etc vary a lot. But I can already tell you, it won't be cheap. Even though you will go with the 'cheaper' solution.
Around 400$ at least I'd say, if you want to include CPU as well.