That color morph used to be $40 from Live Aquaria or Blue Zoo and they were pretty common. However, I don't remember the last time either had them in stock. When you consider that this one is an established specimen, then the price increases significantly and I think it's within the ballpark of what someone would be willing to pay.
I'm sure that a lot of us have paid less for the gigs that we have, and we're talking about more colorful ones and not a common tan gig. But these days, particularly given their rarity and popularity, LFS and other retailers are pricing based on demand and what the market will bear. I've seen prices double and triple.
Furthermore, the entire process of QTing a gig from start to finish has a price tag. Even if you pay yourself near mimimum wage for a week of QT ($15/hr x 2 hours x 7 days = $210), plus the cost of supplies (primarily just salt water) you can easily add $250 to the cost of the anemone. If you add in the failure rate, even if it's just one, you double that price and you're right at the $500 range for a gig.