Fine! Since nobody cares to answer so I did look up by myself and find Clair air purifier (go-clair) which both models have 2.4W and 5.3W at high mode respectively. That means if I let it on 24/7, one Clair will cost me up to $3 per month. Such a nice deal!

Plus the filters are easy to replace and it does not produce ozone as well...