99% of the tires shop will quote you 30 bucks for the front camber screw and nut.

here is the answer to your question:

1) Do camber need to adjust every few months?
a : probably few month or even a year or so.
depending on the tires wear / road condition and driving style.

2) Is adjust camber price RM 30? not even a nut change, it is juz adjust.
a : yes. that is their standard price for workmanship. the only different is some shop do it better and some other,
lousy!

3) the lower arm i change is some other brand, not the original parts, n i ask the mech y not take ori, he said more expensive n not reliable. i was like "wut? original part not reliable?". do this lower arm cost so much?
a : you did not mentioned what is your ride but cheapest after market lower cost in the region of 1xx.

4) Any good tyre shop o workshop do sifu2 here recommend tat it will do a good job n honest? i am tired of kena con here n the
a. There are few. look for nestum or cheeann in garage sale. else, look for highly experience maddriver @ bernard.