To achieve good soundproof, it really depends on your budget for replacing windows.
The price varies a lot.

Please look for laminated or double glazed windows glass.
This will perform better than typical windows but the price can be easily >200%.

The cheapest solution is to buy rubber strip to seal your current windows edge, no windows replacement.
Otherwise, please look for windows, glass or aluminium contractors (German window, Reliance Home, or etc).

There is no "standard" condo size.
The price depends on frame materials, glass type, thickness and etc.

Let's give some examples:
* A "normal" 3' x 4' windows (2 panels), 5mm, around RM300-RM400.
* A laminated glass 3' x 4' windows (2 panels), 6-8mm, with high performance frame, around RM500-RM800.

Not sure about double glazed as I have never bought it.
Please expect slightly higher price than the examples above.

I have never used German windows but heard many good words about them.

And I do believe it also commands a premium price.