I think the varation is by store and how much their supplier charges them. I've seen a $50 dollar 4" purple at one store, and literally the next LFS about 5mi away had a small 2" purple for $120.
Let's not bash SWF for the purple tangs they put up. It's rare enough now that SWF lists fish in that section
..... They fully disclose their condition, and HLLE is fully recoverable with a bit of TLC.