"purple" strains generally are less potent than strains that don't get too purple. Purple doesn't mean the bud is good. It means the strain is genetically predisposed to turn purple. Most "purps" you find are only purple because the temp was dropped during the budding phase of growth. "authentic purple haze" doesn't exist anymore, but you can find "haze" that was flowered during a temp-drop, turning the buds purple....Same with the "purple kush"

Also, names mean absolutely nothing unless you know a lot about the genetics of a plant (example: AK-47 has none of the same genetics as AK-48.....a better example: genetically pure "Durban Poison" compared to the version of "Durban Poison" sold by gypsy nirvana, which is actually "Durban Poison X Skunk #1"

Bottom line, don't trust strain names unless you're growing because then you can buy seeds from a reputable seedbank and research the genetics as extensively as you please.

To answer your question, I've paid $100 for an ounce of purple buds (mids), but I've also paid $280 (well-grown, unbricked sinsemilla).