It depends on a few things. For example, although electricity is a secondary cost associated with running an air purifier, the energy efficiencies of the device will impact how much it costs to operate. You’ll also need to buy new filters from time to time. If you invest in a high-quality HEPA filter, you will have to change it every 3-5 years. There are cheaper filters available, but they’ve been proven to be less effective and need to be replaced more often.