Look on page 8 of this thread for a recipe and photo of shrimp and andouille muffin cakes. LINK
You have to make a lot of them for 200, but they are worth it. They can be made ahead, refrigerated and reheated easily. I've even baked them, frozen them and reheated them. They're fine rewarmed and even at room temp. People have just loved these.
Do you need a warm or cold item?
You could cook shelled shrimp in a bbq based sauce like Emeril's recipe, for example. Take one shrimp and put it in one of the warmed phyllo cups, which would be a little like eating the bbq shrimp with French bread if you get my drift.
You could do something similar with shrimp tossed in a remoulaude sauce.
You could take some andouille, cut it in bite sized pieces, brown it and drain a bit. Then, after cooled, get some puff pastry, roll it out thinner than it is. Roll it around the andouille, bake it, put toothpicks in each one and serve with some various mustards or nothing at all. We do some "pigs in a blanket" with good sausage or andouille and puff pastry. People will eat them up.
You can made a chunky (seafood chunks) crab, shrimp and/or crawfish stuffing for mushrooms and bake them in a butter/wine/sherry or brandy mixture.
You could marinate crabclaws, drain and serve. My Mom did a few pounds, last night for a party and they were eaten in about 10 minutes. Very easy for a large group.
Mini crab/shrimp or crawfish cakes can be made ahead and rewarmed in the oven. I'd offer a remoulaude sauce, white or red or Cousin's Creole Tomato dressing which I use for the shrimp and andouille muffin cakes.
The crawfish pies in phyllo dough was suggested above.
Hard boiled eggs stuffed with shrimp remoulaude.
Mini brochettes-shrimp wrapped on bacon on toothpicks or shrimp and an andouille slice, together.
Shrimp dip in a phyllo cup with a small whole shrimp on top.