Liveries and tunes are counted separately. It’s possible to be legendary on liveries but not tunes, or tunes but not liveries. Whichever one you’re legendary at triggers the increased price mechanism. Unless you’re legendary at both, in which case the vehicle being sold can either have your tune or your livery.
Of the two, tunes was WAY easier/faster. Liveries get less engagement in my experience.
One side effect of my suggestion below would be more transparency on progress (as most badges tend to have a progress visible):