You have to account for the fact that they have paid something for that coral, then they have to account for overhead of the store (salt, water, filtration systems, electricity, payroll, rent, etc, etc) and still try to make a little bit of profit........
Almost all my corals have come from banking trades with local club members, frag swaps, craigslist, etc. Great deals are out there.... best advice I can give is try to find a local forum/club to connect with people around you. I think the most I've paid for any coral in my tank is $20.
Wanna calculate the cost of that new reef tank?? Take your worst nightmare, double it, and you're halfway there.