Too many people use incorrect vocabulary. ‘Cheap’ brings visions of miserly Ebenezer Scrooge, eating gruel in a cold lonely room. In this case, Scrooge might just ignore aeration control and foolishly watch his harvested grain rot.
This farmer / engineer is, instead, frugal in use of his time and money. Say that he buys the commercially offered aeration control at $80k. Something goes wrong, what is his after-sale tech support and at what cost? His own system, built for 1/800th the cost, may have fewer ‘bells & whistles’ but, then again, his install may not need them. Failure of his system is his own responsibility and, like the build itself, costs him irreplaceable time & effort, aka ‘sweat equity’! Still, being the builder, he may find the fix faster that that help desk guy, Steve, in Bangalore (India)!
Just an opinion but I like frugal!
Frugal bastard is better than cheap bastard.
I will work with his family (not us) on what to call him.