Comment by MrMcCall
(< $1000 category)
Living in American public housing, we used our pandemic stimulus money to buy two RabbitAir MinusA2 HEPA air purifiers. At $600 each plus $95/yr (for filter change) they're utterly fantastic and the pre-HEPA stages are easily cleanable with a cheap air compressor and wet paper towels. The multi-stage filter system is quite quiet on level 3 (of 5) but will really blow at 5 and be nearly silent at 2. You can tell how well they work by how the filters build up over time. The build quality is top-shelf with exquisite tolerances.
I can't recommend them enough. In my travels, I learned my favorite aphorism, which comes from China, I believe:
>>> Pay a lot, cry once.
Our RabbitAir units are the finest example we can afford, easily our best quality-of-life investment.
If you're into DIY it's possible to make a cheaper, more efficient and quieter air purifier than many consumer models. From what I understand the problem is that most devices on the market are designed to be small, which reduces the filter area and that again requires a stronger (louder & less efficient) fan. Going DIY also means no dependence on a specific brand's replacement filters.
Then again that doesn't mean off-the-shelf products are bad, for a single room even quite cheap ones can do the job. And they don't look like a fan taped onto filters, so there's that.