I know the issues with this LFS
...but Fishtown in Flushing has a gorgeous purple tang about 4" for 129...acclimate him well and you're okay. He's brightly colored and I saw him eat well.
I'd say $100 and under is a good these days. I feel like lately the purple tangs are coming down in price as there seems to be a lot more of them for sale around. Supply and demand.