It took three tries, but I finally managed to cobble together a DIY air purifier for VOCs that my home VOC sensor (wildly inaccurate, but directionally useful) claims is sufficient for my space and VOC exposure.
A giant carbon canister, a vacuum HEPA filter, two PC fans (I started with one and upgraded based on sensor data).
This is ONLY for filtering VOCs (smoke/gas), it is NOT useful for COVID.
Parts in next post.