Normally, plaster ceiling installation would be cost around RM2 per sqft (plain type). Box, L-box and cornice will be added additionally.

Lots of folk sometime forget plaster ceiling drive up lighting cost because you need to re do the lighting wiring. Those lighting point wiring will be expensive but the down light itself is cheap.

AudiA6

Square down light with glass cover is only RM22 (6in) with 1 GE 18w bulb. RM32 for double bulb.

Dirt cheap nowaday!

Top 10 is just beside Tesco Puchong, corner lot.
Perfect Lighting is at Uptown Damansara facing LDP, u can see their signboard got a big yellow bulb there. The map http://wikimapia.org/#lat=3.136456&lon=101...91&z=17&l=0&m=b
I found Perfect Lighting prices are cheaper even though Top 10 more famous, but Top 10 have more choices for hanging lights and ceiling fan.

Square type is more expensive than Round type, and some square can put 2 bulbs.
There are alot of combinations, square/round, size 4"/6", got cover/no cover, material aluminium/chrome/metal/stainless steel, with balast/no balast.

Functionality is more or less same, appearance is subjective. Of coz personally i feel square type is nicer and stainless steel is better too but higher price.
Practically and $$ wise, i prefer round shape 4" with no cover and no balast.

Reasons?
Round shape - Square shape is harder to cut the plaster ceiling compare to round (contractor might charged higher for installation)

No cover - If got cover, it is hotter, ur bulb life might burn easier. Harder to change bulb coz need to open the cover and normally cover will trap alot insects inside.
4" - Subjective choice coz i think 6" too big 

No balast - Generally light with balast will last longer but harder to change. And if u do looping wiring of few lights, one of the balast spoil, u need to troubleshoot which 1 spoil coz all the lights can't be turn on. If no balast it is easier to change urself if anything wrong but the life is shorter.

Material aluminium - Stainless steel too exp, metal will rusty, so i get aluminium.
For energy saving bulb, u have 3U or spiral light. 3U is cheaper price. Normally the wattage is around 18W-20W, of coz if u want brighter u can buy higher power.

Brands u got Philips, Osram and GE, of coz those cap ayam brands also. Personally i prefer GE becoz the quality is better but more pricey. It is harder to find in light shops too. Most will carry Osram and Philips. If u want save, buy Philips, this batch Osram really screw up in quality, the bulb burn frequently, ask in those lighting shop u will know.

Color, u got white, cool white and warm white. In laymen term, those yellowish light we saw is warm white, white color is white and cool white is like those Mc.Donald restaurant light, in the middle of yellow and white. I prefer cool white but the only famous brand has cool white is Osram so I give it a miss, unless u want try those cap ayam brand. Else, u might try to mix some white and warm white.