This led me down a rabbit hole of ancient Roman pricing information! Turns out that a pair of purple silk pants (it seems purple dye was reserved only for silk) was actually closer to 2000x more expensive than standard (wool) pants. Also, the penalty for commoners wearing it was death, so there's that.
>Therefore, the dye can be collected either by "milking" the snails, which is more labour-intensive but is a renewable resource, or by collecting and destructively crushing the snails. David Jacoby remarks that "twelve thousand snails of Murex brandaris yield no more than 1.4 g of pure dye, enough to colour only the trim of a single garment."[14] (from Wikipedia, Tirian Purple //
It's my understanding that it was a badge of the senate, so wearing it would be like impersonation of a senator. Or worse, impersonation of the Emperor.
I am suspicious of the 12,000 snail number. I see that people nowadays who make a similar dye from snails called tekhelet need around 30 snails for each yarn they dye, which I would guess would extrapolate to the 12,000 being for an entire garment.
But that pricing gap is almost entirely uncoupled from material cost.
They make them by hand (by choice), and of course use the best materials, but a cashmere shirt at H&M is very cheap. Brands are priced out of reach of common folk, but materials and types of clothing aren't.
Maybe it was a heuristic for theft? As in, "as a commoner, there's no way in hell you could legally get your hands on a pair of these, so you must have stolen them from someone else".
There were actually laws, in many different times and places, know generally as "sumptuary laws". Wikipedia has what looks like a good overview: https://en.m.wikipedia.org/wiki/Sumptuary_law
It doesn't seem to say much about actual enforcement, other than the lack of it for Louis XIII's decrees, and the repeated (and apparently ineffective) calls for stricter enforcement of the English laws.
