I made mine from a paint pressure vessel for about £60, plenty of you tube videos on the Harbour freight version. Beeen using mine for a couple of years now, and works a trat up to about 80 psi.
Long shot but try going around to auto body shops and see if they have any old ones they aren't using anymore. Many have gone to airless and don't need the traditional pots anymore. Your local second hand selling site might have some too.