Well, you would want to take into account what you are looking to do after graduating. I do not know much about the NUS and IESE rankings, other than that they are both top 25ish. Are you looking for Finance? IT? Consulting? Marketing? If either program is much better than the other in what you are looking to focus on, then that may be the school you would want to go to.

That being said, if both schools have good programs in your career focus, I would honestly say go to NUS. The only reason I say this is, from what I can see, the two schools aren't too far apart from one another in ranking. And if what you say about IESE being over twice as expensive as NUS is true, then you may want to go to NUS. As you know, a big part of evaluating the value of a B School is not just the school's rank, but also how much salary you are giving up to go added to how much debt you are taking on when graduating. It does appear that IESE is the more reputable school, but if you can save THAT much money buy going to NUS, it seems to me that it would be worth it to do so. NUS is still a GREAT school (top 25 globally on a consistent basis), and as long as they have a good program in what you are looking to focus on, saving that amount of money may be more beneficial than going to IESE.

If you have IT experience then going into either wouldn't make a difference, better go for a lower cost option - NUS. This is because post graduation most people with tech background have to come back to India for jobs.