im currently using a simple well pump switch. i got it for round $10 at a place called contractors warehouse. it works,but lets the pressure drop to almost 60 psi before kicking back on,so it cycles between 60 and 130.
you canget an actual air compressure pressure switch for around $15 from a place called "surplus center" ill try and dig up a phone # and part numbers for ya later
i plan on upgrading mine to keep the pressure more in the useable range/ air tools dont work so well at 60 psi