Corsi-Rosenthal - I like that setup. Though the prices of filters themselves have gone up considerably. But with 4 large filters, they ought to last quite a long time. I change my furnace filters every 2-4 months, but these should last even longer, I think.
If I didn’t have the AI air filter/purifier with the UV light that likes to scream at me when it needs something, I’d build one. I also like the setup.
Also, with more air space inside the cube of filters, I’d think the fan would work better and maybe not work the little motor as hard. You can buy the filters in 4-packs, and they are cheaper in bulk.