If you qualify and still can manage, I'd say $300k can be invested in SG properties as downpayment. Yes prices are high already, but between SG and Iskandar, I am more confident in SG. Besides, you don't face currency risk.
But if you are getting old, no more direct income from work, have S$300k cash and want to retire somewhere, maybe I see your point of spending it on an Iskandar property. But I won't call that an "investment" as the time line is too long to predict what will happen and there is no clear direction where it is heading. Anyway, I'd think about the possibility of renting first and using the leftover money for other investments.
xebay11 mentioned something really good for you to think about. By putting $300k in a RM FD, you are guaranteed a good compounded growth of 4%. There is currency risk here. But even if you buy an Iskandar property, you are faced with the same situation. Actually it's worse.
With a property, there's a question of the future resale value. I know many are extremely bullish thinking their properties will fetch good money next time. I say, Don't be so quick to assume. You didn't buy it way back before 2013. The prices of Iskandar properties have inflated a lot in recent years. But salaries have not. And there is oversupply. These are all risks you have to mitigate.
In other words, you can't liquidate your property next time so easily if you need to. Making a loss is one thing. But if no one is interested to buy means you are stuck! You can kiss your S$300k goodbye and maybe ask your kids to try to sell it away after you pass on.
Of course, if like some here, you insist "I'm buying for my own stay so I don't give a damn whether I can sell or I will make a loss next time", then there's nothing worthy to discuss here. It's your money after all. But I wouldn't buy something big like property and not think about whether I can let it go even if I have the money. Or maybe I don't have that kind of big money yet to throw away like that!