Wildfires have become more frequent and severe, and evidence showed that exposure to wildfire-caused PM2.5 (fire-PM2.5) is associated with adverse health effects. Fire-PM2.5 exposure occurs mainly indoors, where people spend most of their time. As an effective and timely approach of mitigating indoor PM2.5 pollution, air purifiers incur notable associated costs. However, the long-term global population exposure to indoor fire-PM2.5 and the economic burden of using air purifiers remain unknown. Here, we estimated the indoor fire-PM2.5 concentration and the cost of reducing indoor PM2.5 exposure, along with the extra cost incurred because of fire-PM2.5, at a resolution of 0.5° by 0.5° globally during 2003 to 2022. Our findings revealed 1009 million individuals exposed to at least one substantial indoor wildfire-air pollution day per year. We identified pronounced socioeconomic disparities in the costs of mitigating indoor PM2.5 exposure, with low-income countries bearing a disproportionately higher economic burden, emphasizing the critical need for addressing these disparities.