--give about a 1:5 to 1:8 conversion factor for alpha lipoic vs. r-lipoic (though I'm not sure just how some of these studies make this determination other than trying different amounts and surveying users as to their subjective sense of symptom reduction).

A 1:6 ratio is often cited--100mg of R-lipoic is roughly equivalent in effect to 600mg of alpha-lipoic. (That would help with the expense issues if relatively accurate across people). I myself went from 600mg/day alpha to 100mg/day R-lipoic without appreciable symptom difference.