I suppose there are Corsi–Rosenthal box designs out there for 3d printing. We don't have filters like this here, otherwise I'd make such a diy purifier instead of buying one

But then you still need to spend 70 pounds on a filter!

They make round HEPA filters for shop vacs that are in the $20-30 range. The hard part is finding a fan that works well at high static pressures. I've had good luck with NF-F12 PWMs.

When you need static pressure, use a centrifugal blower. I've got one on top of a HEPA shop vac filter from harbor freight, some hot glue seals it up nicely to a thin plastic sheet I cut as a size adaptor.