Retail seafood in MKE?
Some of the Sendik's locations (the ones owned by Balastreri) are having a seafood sale today; when they have them, the prices are always very very good. If you get on their mailing list, they will email you in advance of these one-day sales.
And then there's Empire Fish on Watertown Plank Rd. They can also be pricey but the quality is first rate, and the variety is pretty good.