I built a belt driven compressor that runs on 12v. It is my (much simplified) take on the voltair compressor ($1600) and my version is around $400.
It uses the following
Harbor Fright replacement pump $130
Electric winch motor $80
Welded metal frame $40
Air hoses / fittings $75
Square D pressure switch $40
It charges my 20 gallon tank in under 4 minutes to 130 psi from 0
It goes from 90 to 130 in about 1 minute
It’s not very pretty and it’s rather bulky but I wanted proof of concept.