It really depends on what you want.

If you are getting 5.1 for movies, then make sure the woofers for the fronts and center are similar in size and characteristic

Usually the rule of thumb is that the cost for the 2 fronts and center is 2 to 3. If the fronts are NT2000 a pair, then the center should be about NT 3000 dollars.

Do not save on the center because it is where all the dialogues come from when you watch a movie.

Buy them in the following order:
Fronts, Subwoofer, Center, then the Surrounds