Air con

Ok...I am a self confessed clueless person when it comes to air cons and other mechanical gadgets etc..
Currently, i have 3 very old wall mounted daikin air con units (dunno what the correct name is.) They share 1 compressor and i was told by my air con serviceman that the reason why my electricity bills are so high is because they are all connected to only 1 compressor and that i should have at least 2.
So, i have been looking around for new aircons and all i want is something from a reputable brand that is energy efficient. Anyone can recommend?
Roughly how much would it cost for me to change the compressor + 3 air con units?

Thanks.

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