I got an old freezer compressor for $NZ 15, switch second hand $NZ 5, 1/2 hp Hoover capacitor start motor (and blacksmiths wall drill) $NZ15, I had an old aircraft low pressure oxygen cylinder. Put it all together, about half a day, its a good one, but a bit slow for some things.
Just got to repair the switch on a second one that I was given, that will improove the capacity. All that for less than 20 pounds. Ian S C