The calculation should be in this way.
Buy 1 good air purifier with 4k and its performance is equal to 8 normal air purifiers.
But if you buy 8 normal air purifiers, the price is about RM700x8=RM5600
It's still worthy to consider to buy 1 good air purifier, right?

Also, you must bear in mind that the function of air purifier is to filter air and to provide clean air to breathe. As what I had said, if you buy a normal air purifier which fails to filter air fast enough to let you breath clean air, why waste that money? It's unless every time when you want to breathe, you inhale very close with it and that seems impossible.

Hi Purtaskyline,
don't be confius with this 2 item. Air purifier main function is to REDUCE a surrounding dust in your room and trap all the dust inside the HEPA filter, REDUCE the odor/ smell coz they have a carbon filter inside.  an Ionizer is just a accesories to the air purifier (like a vitamin to air air).

Before you make a purchase of air purifier, a few thing u have to consider.

1. Where are you going to use this machine (bed room / living room)
2. How big is your room size ( machine come with capacity area)
3. What is your main concern ( dust, odor or what?)
regards
DR IAQ 

I have doubt about this matter. How reliable is air purifier/ionizer since it involve big amount of money from RM 400-2000? Lets say I have small room and when somebody sleep there, the room was warm, smelly and dusty, if I put Ionizer inside the room, the air flow will be treated? Also I read from the product said that 99.9% no dust inside the room. is it true? Someone has try thsi product can share their experience here.

Thanks.