£45ish for the GPU block, thats a full cover one that cools the VRAM as well, from someone like EK, or you can go the GPU only route and stick some RAMsinks on the VRAM, probably cheaper, although not that much.
£40 ish for a top of the pile CPU block such as the D-Tek Fuzion + nozzle kit, or the Swiftech Apogee GTX.
Rads, depends on how far you want to go...My personal preference is the Thermochill PA series because you can use them with silent fans and still overclock like a mentalist

They are large (thick), expensive and quite fugly with a rubbish paint job.
The best thing to do is google your case and find what other people have done with water setups, and that will give you a good idea where to start...sometimes, cases just dont do watercooling well.