Not sure price shopping is all that wise when it comes to livestock. Spatulas and baked beans, maybe I'll price shop. You want someone that's spent some resources on your fish so you get healhty fish, not someone who's trying cut costs, take shortcuts and pass the buck on to you.
I dont personally see anything wrong with making sure youre not being charged way too much on anything. Just because one store charges more doesn't necessarily mean youre getting a healthier fish, with the exception of stores that charge more because they quarantine fish before selling them.
How much these fish normally go for is likely going to be different based upon where you live, but my favorite fish store will sell juvenile emperors for under $100 and small purple tangs for under $200.