Why would you need a suit at 17? That aside, you wouldn't want to make the mistake many of us made with a first suit. That means making an ill-informed purchase of an ill-fitting suit probably with gaudy detailing.

I know you're thinking Topman or Zara but if the suit is not that urgent, maybe you should look around the internet more to develop your taste in suits (because they will definitely change once you've seen 100 suits). If you're close to sample size like me, buying a suit off the rack wouldn't be as bad as some people say they are. 

Yes, RM600+/- is do-able. Padini's cuts are getting quite slim nowadays, but less 'contemporary' than Topman. Zara is like the classier version of both. There are other brands like Domanchi, TSS, and shops selling low quality but very 'korean cut' suits.

Points to ponder:

You're 17. You are not 100% sure whether you will grow anymore. Whether vertically or horizontally.
You might grow a belly in college. Or you might decide to hit the gym.

My advice is, better not invest in a suit thinking it will be a long term investment, for now. Instead, go for something that is decent, but still affordable enough, relative to your financial status.