Aluminum Frame PC Fan Corsi-Rosenthal Build (2023)
itsairborne.com
itsairborne.com
About the same as a Coway
Files can be purchased by backing the Kickstarter but they won't be sent until November: https://www.kickstarter.com/projects/joelcreates/oddcube-air...
I think this could be substantially cheaper than a build based on a PC case.
https://www.filterboxbuilder.com
There's no real performance difference between DIY and metal PC fan filter boxes, just durability.