The filter cost for the AirFanta 3 doesn't seem particularly high? In fact it seems cheaper than competitors.

All the purifier companies realized they make more money selling overpriced filters, so $60+ for the OEM filters is common nowadays. Despite it just being a standard HEPA filter cut to a specific size.

Airfanta 3 Pro filters (four) - $57

Coway Mighty Filter - $60

Coway Mighty2 Filter - $70-$80

I'd be concerned about the availability of filters after a few years. Some of these companies have been changing their models and filter type every year to add some nebulous feature. Others just go out of business.