I had the same insight for in-home air movement. Purpose built inter-room fans from broan/etc are 3x louder and several times more expensive than computer fans at the same CFM. I've been very happy with them.
https://scosman.net/blog/using_in_wall_computer_fans_for_hom...
Vevor makes drop-in floor/wall register fans in the $35-40 price range. The 'proper' solution is inline booster fans in each leg of the ducts, but retrofitting can be expensive depending on access.
if you have house (with attic), jump ducts are nicer solution
There are continuous extraction fans, they're called dMEV systems. Eg https://www.epicair.co.uk/products/vent-axia-lo-carbon-reviv...
There's also systems which can move air both ways through the whole house - https://www.ventilation-alnor.co.uk/index/support/alnor-know...
Your DIY solution looks a lot cheaper though.