A DIY air filter is pretty easy to make - you just need a box fan and a Merv 13 or higher filter. They worked pretty good for us back in 2020 once we returned from the coast. (It took me forever to find a MERV 13 filter though)
https://pscleanair.gov/525/DIY-Air-Filter
https://www.montanawildfiresmoke.org...ilter_2020.pdf