Break even point for 120k at extra 300/month? Are you kidding me ?
MBA is a long term investment, you might can't see its value when you're in junior post. But when you're climbing to the Managerial post, MBA tag will give you a good lift. 
Extra 300/month is not forever, you've gained up working experice, the MBA qualification in your resume definitely will grant you better 'demand power'
My friend a MBA holder, able to get senior exec. post in a top local bank after he grad. Which might took a degree holder 1-2 year+ to reach there.

I talked with an older gentleman who is holding an MBA and has a fairly high position in the corporate world.

His perception on the matter is that for Malaysia, an MBA only matters when you reach a certain level in the corporate world, normally attained after 30 years of age. Before that it would not make much difference. The advantage it confers is that at a higher level, it makes moving up easier as the added prestige is there.

So for fresh grads, it wouldn't have any point at all.