Does the ozone come from a air fed machine? Or does it have to be pure medical grade oxygen? If not, then PMA look online for an affordable air fed unit...I really wish someone would make an affordable medical grade unit. I would love to experiment with ozone..
If using it externally most machines can be used with air. Cold corona is still preferred to avoid the acids, but a weaker hot corona is fine. The amount of acids produced will be negligible as long as the unit is not really high power. Chances are the unit you will find is not going to generate much acid. Units used to ozonate pools can generate enough acid to burn tissues, but these units are not cheap. Units under $600 are generally low output.
Keep in mind though that if using air this is ONLY for external, not internal use.