Before you base your decision solely on cost, I cannot stress how much that you trial the headsets on first. I was going to buy the Sennheiser S1 but it sat so uncomfortably on my head - almost perched - that I tried the Bose and the Zulu - after all, the headset will be on your head long after the additional cost / saving has been forgotten.
Based on that, I bought myself a pair of Zulus and am very happy with them. If they all fit, then it's a question of whether you value the Bluetooth streaming function of the Zulus (I love it, it really aids break the monotony of longer flights alone) or not or whether you want to pay more for, in my mind, equal noise reduction......