Cheapest option is the Hatari one for just below 3000 Baht. Because I buy pm 2.5 fabric that I cut by myself to add it in front of the original Hatari filter, thus extending the life span of the Hatari filter by 500%.
Effectiveness is 100%, meassured with my pm 2.5 meter...
Just for our 60m2 lobby/living room we need 3 purifiers to get pm 2.5 to around 5 ppm on days when outside pm 2.5 exceeds 50 ppm...