NOTE: price seems to vary by location.
In Google Express, Costco has the Winix C535 air purifier back in stock for $139.99, but in some places like San Diego and Los Angeles it's appearing as $99.99 . Using Google Express app, put in promo code APPANDSAVE20 to get 20% off, so should be $119.99 for most but for some like me it was $79.99.
Winix C535 is same as Winix 5300-2, except it is white instead of dark gray and comes with an extra years supply of filters.
I have the 5300-2 and it seems to work well. It is not supposed to produce ozone but I turn off the "plasmawave" feature anyways. It is very quiet at low settings and has a "sleep" feature that turns off the air quality indicator light. My kids farts and in-diaper poops have turned it from good (blue) to yellow or red (bad) so I think it works! I ordered an extra one for upstairs just now using this code.