What's a fair price for sashimi in the Boston area?

I'm talking about slabs of fish in 1/2 pound packages in a market, not about prepared food in a restaurant. I live in Somerville, if that makes a difference. I like tuna, salmon, yellowtail, and mackerel. Don't bother writing in with the price of sushi rolls, octopus, cooked fish, or with the price on the West Coast.