Hi Nigel
It is generally not the cost of the floodlights that you should consider, but the switching/control equipment, look at the GJD or the Voltek, they will both take more than one PIR, as for the brightness that will depend on the size of the bulb you fit, most come these days with 400Watt but if you wanted to you could fit a lower wattage.
Both companies are external lighting manufacturers, so the equipment will have IP ratings
Hope this helps you come to a decision