For the cpu and gpu on the same loop I'd probably want to consider a 360mm rad (triple fan). A 240mm rad may do the trick but keep in mind the h100i and similar aio's are using a 240mm radiator for the cpu alone. If this is meant for the cpu and gpu both down the road it needs to be considered up front hence the 360mm suggestion. Otherwise that kit Gam3r01 linked to is a decent price.
Hard to say on individual parts, things like reliability and performance go hand in hand with cost (for the most part). Cheap parts, less reliability and performance, higher performance higher cost. It can quickly add up to several hundred, anywhere from $70-100 for a cpu water block, another $80-100 or so for the 360mm radiator, figure $15-20/ea for the fans with a min of 3 fans, 6 if you want push/pull. Another $75 to $150 for pump/res combo. Coolant, tubing, fittings may easily run another $25-50. Without even going top notch premium components it can quickly jump up into the $350-400+ range.