Take netmatrix's suggestion. He has the best knowledge around here on where to get budget garments.
Although, I'd advise you to top up a little more to maybe around RM120+ and get one from our local brands such as Padini / SEED since they have a more modern cutting compared to SUAVE or those in Kamdars' (tried them on last time but the fit was not suitable as I'm quite slim).
Note: waistcoat and vest is actually the same thing - with the former being a British term while the latter is an American term. The American term is more widely-used by fashion retailers nowadays but some Britons might still interpret vest as tank tops and whatnot.

Go to Jusco and look for their in house brand SUAVE. Got many designs since few months ago. Some look like they are Korean look inspired. Less than RM100. Or if you are really cheapskate, go to Mid Valley look for Kamdar and the vest is less than RM20, but looks very dated.