Makes 6 servings at $2.66 each. Prep: 20 minutes. Chill: 1 hour. Cook: 8 minutes.
Grind crab boil (pickling spice) in spice grinder or with mortar and pestle until almost a powder. Place fish in large bowl with lemon juice and ground crab boil. Refrigerate 1 hour.
Shake together cornmeal, flour, salt and pepper in paper bag to combine. Remove fish from marinade. Using pastry brush, spread both sides with mayonnaise. Place a few fish at a time in the bag, shaking to coat.
Heat oil in large, heavy cast-iron skillet over medium heat. Working in batches, add fish; fry 4 minutes on each side, until golden brown. Transfer to paper toweling to drain. Keep warm while cooking remaining fillets.