Xiaomi - Mi 3C

I have a Xiaomi air purifier, and it's able to talk to HA locally over WiFI. The current mIOT integration supports a bunch of products locally. You will need to create a xiaomi iot account for initial setup.

https://www.amazon.com/Xiaomi-Purifiers-Efficiency-Intelligent-Purifier/dp/B08LH7XZ3H. This one but the amazon listing isn't available anymore. I think the new ones also support it. Also I believe have different devices available for different regions. I also have a Levoit purifier but that one requires a cloud connection to integration with HA, no local options afaik.

FYI HEPA filters are basically marketing BS in the consumer world. Very few filters with "HEPA" in their description are actually capable of meeting HEPA standards. $400 for a 200sqft capable air purifier is crazy. I have a Levoit core-300 for my 100sq ft room and it clears out my vape smoke in a matter of seconds. I believe its possible to get activated charcoal filters for this to help reduce odor, if not you can find activated charcoal sheets or packets to put inside the air path. There's a community supported HA integration for Levoit, but its reliant on the cloud service. You can flash the Core 300 with ESPHome though and have it work completely locally. I also have a Xiaomi Air Purifier 3C, it also relies on a community maintained integration with Xiaomi Miot but it can work locally too, I know cause I have it blocked from internet access and it works fine. There is also a way to flash ESPHome on these, but I haven't tried. I'm using that one in my living room which is somewhere around 800 - 900 sqft but its a double height living room so there's a tremendous amount of volume there. Side note, make sure you've looked at fixing other parts of your house before getting an air purifier. Make sure your AC ducts are clean, and the filter for your AC is working properly. Though don't put a high MERV filter in there unless your air handler is designed for it. You can actually filter more without putting extra stress on your air handler with thicker filters, but in my experience its rare to see units that can hold the thicker filters without modification. Also make sure your windows are sealed properly.

Xiaomi 3C as a central unit in the living room, xiaomi 4 compact in bedroom. Have them running on full blast during the day and whenever I come back home the air inside actually smells clean. Air purifiers are essentially just a fan that sucks air into a HEPA filter, a laser detector in the back to detect air quality, and optionally a few other bells and whistles. The differences between the brands are gonna be minimal, just look at the sq.m. Rating on them. The pm2.5 levels on the AP are usually not that accurate so best invest into a dedicated pm2.5 tester to get more accurate values if needed. Or you can just do what I do and have them on full blast during day and on auto at night. I went with xiaomi as they have pretty good reviews and are cheaper than other brands like Philips. After having used them they’re pretty good value over all. Got the 3C around 5 years ago and it still works well, 4 compact is also great especially for the 1.8k I got it for.